BVOPT – 601 CONTACT LENS II

Learning objectives:
To Learn:
 Soft contact lens materials
 Properties of contact lens material
 Manufacturing methods of contact lens
 Pre-fitting examination
 Soft contact lens fitting
 Soft toric contact lens fitting
 Insertion and removal of soft contact lens
 Rigid lens insertion and removal
 Do’s and Don’ts of lens care
 Contact lens care system
 Follow up visit examination
 Complications of soft contact lenses
 Therapeutic contact lenses
 UNIT 1
CONTACT LENS MATERIALS
Ideal Contact Lens Material
The ideal contact lens would:
 Provide sufficient oxygen for normal corneal metabolism.
 Be physiologically inert.
 Be very wettable on the eye.
 Resist lens spoilage, especially deposit formation.
 Maintain stable dimensions.
 Be durable when handled by wearers.
 Be transparent with minimal light loss.
 Be optically regular so its optics are predictable.
 Have physical properties which allow the creation and retention of high quality surfaces.
 Require minimal maintenance by wearer.
 Be easy to fabricate lenses from.

Important Material Properties

 Oxygen permeability is a material property and not a lens property.
 Good wettability is necessary for long-term lens tolerance.
 Scratch resistance is essential to the maintenance of good optical surface properties.
 Rigidity (rigid lenses) is a key determinant of the minimum lens thickness necessary to resist lens
warpage on the eye, particularly if the cornea is astigmatic.
 Material must be stable if lens parameters are to remain as manufactured.
 For comfort, good vision and minimal adverse responses, the lens must resist deposits.
 The lens should withstand normal handling and wearing, i.e. not break easily.
 Flexibility (soft lenses) is also a key factor and should allow the lens to conform to the ocular
surface.

Physiological Properties
One of the most important properties of a contact
lens material is its permeability to oxygen (Dk).
This property is an inherent material property (like
Permeability to oxygen
specific gravity or refractive index). It is not a
function of lens thickness, shape or back vertex
power (BVP).
Oxygen transmissibility, Dk/t, is the Dk of the
material (its permeability) divided by the lens
thickness. The thickness t may be tc (geometric
Oxygen transmissibility centre thickness) or tLocal depending on the
transmissibility being calculated.
D = diffusion coefficient of the material.
k = solubility of the gas in the material.

EOP or the Equivalent Oxygen Percentage. EOP

Equivalent oxygen percentage
states the oxygen concentration of a gas mixture
 (the balance is nitrogen and water vapour) which
produces a corneal response equivalent to that
resulting from wearing the contact lens.

Physical Properties
Wettability It is the ability of the tears to form a complete
film over the lens surface.

A drop of pure water is placed on the test surface.

The angle between the tangent to the drop’s
surface at the point of contact and the horizontal
test surface (θ {theta}) is measured.
 a zero angle = completely wettable
 a low angle = somewhat wettable
 a large angle (especially>90°) = poorly
wettable.
Flexibility The, more the lens is rigid the less it will bend
when placed over the cornea. A highly flexible
material will contour to the cornea.
Optical quality  Material must be transparent with little light
transmission loss.
 Material must be optically homogeneous, i.e.
Its refractive index should not be subject to
regional variation unless such variation is
intentional and well controlled.
Biocompatibility The lens should not induce any inflammatory or
immunological responses and should be inert.
Manufacturing ease The process of lens manufacturing should be easy
and cost effective.
Stable parameters Lens material should be dimensionally stable and
be easily polished. The hydrogels should have
stable hydration parameters.

SOFT CONTACT LENS MATERIALS

Poly(HydroxyEthyl MethAcrylate) (PHEMA)
 Original material (1952-1959, patented 1955) by O. Wichterle and D. Lim, Czechoslovakia.
 A close relative of poly(methyl methacrylate) (PMMA, patented 1934).
 Its differentiating feature is a polar hydroxyl (OH−) group to which the water dipole may bind. Water
content is approximately 38% (W/W). PHEMA is still in regular use by many manufacturers.
A so-called second generation material was the Griffin ‘Bionite’ Naturalens (1968):
 a co-polymer of PHEMA and Poly(Vinyl Pyrrolidone) or PVP, 55% water content
 a direct descendent (vifilcon A), is still in use.
Other Variants Followed Most were a combination of two (co-polymer) or three (ter-polymer) of the
following monomers:
 PHEMA (poly(hydroxyethyl methacrylate).
 PVP (poly(vinyl pyrrolidone).
 MA (methacrylic acid).
 MMA (methyl methacrylate).
 GMA (glyceryl methacrylate).
 DAA (diacetone acrylamide).
 PVA (poly(vinyl alcohol).
In each of these methods, a cross-linking agent is required.

MAUFACTURING METHODS OF CONTACT LENS

Four manufacturing methods are commonly used to produce soft lenses. Each produces lenses with
slightly different performance characteristics.
1. Spincast
2. Reverse process III
3. Cast molding
4. Lathe-Cut
Spincasting
Spincasting is based on the simple concept of changing spinning liquid into a solid contact lenses.
Example of a spincast lens is B&L series (B,U & HO) and Optima 38 contact lenses.
Spincast Manufacturing Process
a) Lens production begins when liquid monomer is injected into the spinning mold (lens geometry is
determined by spin speed and volume of material injected). Spin speed also determines the final
lens power (the faster the speed, the higher the minus power of the contact lenses). The center
thickness of the lens is determined by the volume of monomer injected into the mold, the greater
the volume, the thicker the lens.
b) After spinning, the lens form stabilizes and is polymerized (hardened) under a senes of ultraviolet
lights.
c) C. Next, the penphery of the lens is butfed and polished to produce a smooth surface
d) The lens is then hydrated in a stetile. hot water bath A polymacon (HEMA) lens absorbs about
38,6% of its weight in water, and expands in volume approximately 12%.
The process of manufacturing a soft contact lens by spin casting.
1) A male tool is machined rom stainless steel; the contour of the tool head will def ne the shape of
the anterior lens surface. The same tool is used to make hundreds of thousands of moulds.
2) A female mould is made by pressing the male tool into molten polypropylene , which cools and
sets.
3) The female mould is mounted , with the concavity facing upwards, in a spindle that spins about
the lens axis, and liquid monomers are introduced into the spinning mould .
4) The monomers in the spinning mould are irradiated with ultraviolet light to initiate lens
polymerization.
5) The dry lens is removed from the mould , the lens edge may be polished and the mould is
discarded.
6) The edge of the dry lens is inspected at 10× magnification.
7) The dry lens is placed in saline, which hydrates the lens, causing it to swell to its final soft lens
form.
8) The hydrated soft lens is inspected at 10× magnification.
9) The soft lens is inserted into a blister pack containing saline.
10) The blister pack is sealed with a special oil, and a label is stuck on to this.
11) The sealed blister pack containing the lens is sterilized in an autoclave.
12) The individual blister packs are inserted into packages, typically in multiples of either three or six
lenses.
Advantages of Spincasting
 Spincast lenses have tapered edge profiles and smooth surfaces that enhance comfort during lens
wear.
 These lenses exhibit minimal lens movement on the eye because the back aspherical surface of the
lens matches well with the aspheric profile of the cornea, yet still produce dynamic tearfilm.
 It is easy to fit because it has only one base curve.
Disadvantages of Spincasting
 In some patients, the spincast lens may decenter slightly. this does not affect visual acuity or
physiological performance because of the lens has a large optic zone. However, some practitioners
consider this to be an undesirable characteristic.
Because spincast lenses are thin and flexible, they can be more difficult to handle, especially in low
powers.

Cast Molding
A lens is formed between two plastic molds. These molds are manufactured with the precise dimensions
and surface geometry necessary to mold a lens without additional lathing or polishing.
Cast Mold Manufacturing Process
The four steps in the process include:
1. Mold production
2. Lens casting
3. Lens hydration,
 4. Lens inspection/packaging
The anterior and posterior molds are produced using high precision optical tools.
a) The anterior mold is injected with liquid monomer
b) The anterior mold is then capped with the posterior mold.
c) The capped assembly then travels through a series of ultra-violet lights for the liquid monomers to
become harden.
d) Once the material hardens, the posterior mold is removed (decapped) and discarded.
e) The anterior mold contains the hardened lens, which moves on to hydration.
The lens can be hydrated directly from the mold (polymacon), or dry released then hydrated (alphafilcon
A). The lenses are then inspected and packaged into a blister package. The lidstock on the blister will then
be labelled with the lot number, power, and expiration date of the lens.
The lenses are then autoclaved to ensure the product is sterilized.
Examples of cast mold lenses are B&L Soflens 59, B&L Soflens 38, B&L Soflens Toric, B&L Soflens
MuitiFocal and B& L Purevision.
Advantages of Cast Molding
 Produces finished lenses without the need to polish the lens (as in spincasting) or back surface
polish (as in RPIII or double lathing).
 Produces a high quality lens at a lower cost than any other process.
 Has very consistent edges and smooth surface characteristics.
 Produces a consistently high quality lens with excellent visual acuity and comfort. (Highest
reproducability)

Reverse Process III

Bausch & Lomb has developed a unique process that combines the best of spincasting and lathe cutting
called Reverse Process III. With this process, the anterior surface of the lens is produced with spincast
technique, and lathe cutting produces the posterior surface of the lens.
Reverse Process III Manufacturing Process
a) The mold is placed in a spinning cavity
b) It is then injected with a liquid monomer.
c) Using ultraviolet light, the material is polymerized and hardened, and a casting is produced.
d) The casting is transferred to a computerized lathe that cuts the proper geometry for the posterior
surface of the lens
e) The lens is then polished in a two-stage process to obtain a smooth central surface and rounded
posterior edge following the lathe-cut process.
f) At this point, the lens is placed in a warm hydration chamber and removed from the mold.
As with all Bausch & Lomb lenses, the Reverse Process III lens is subjected to a series of quality
assurance and sterilization procedures.
Advantages of Reverse Process III
 The spincast anterior lens surface is very smooth, giving the lens precise optical quality, excellent
comfort & an ideal edge profile.
  The lathe-cut posterior surface gives optimal on-eye movement & centration.
 Lathe cut allows better control of the lens thickness profiles, so the lens will be easier to handle
relative to spincast lens, especially in low lens powers.
Lathe Cutting
A diamond knife is used to cut both surface of the lens in order to get the final lens. Traditional PMMA
and rigid gas permeable lenses, as well as some soft contact lenses, are produced using lathe cutting. This
process is often referred to as double lathing, since both lens surfaces undergo the cutting procedure.
Example of a lathe cut lens is B&L Optima Toric contact lenses.
Lathe Cut Manufacturing Process
a) Lathe-cut process begins with the material in the form of a button (the button is typically made by
molding liquid monomer into a tube which is then cut into many buttons
b) The button is then placed in a diamond-tool lathe and rotated at a very high speed.
c) The diamond-tool cuts away the polymer and produces precise lens surface curvatures and
geometry The concave surface of the lens is then polished.
d) The lens is placed on another lathe, where the convex anterior surface is cut and polished to the
exact curvature required for proper optical power
e) Edge polishing is then performed using conventional hard lens techniques.
f) Once lathing is completed, the lens is hydrated in saline to make it flexible. In its final form, the
lens is measured and verified for accuracy, inspected tor cosmetic defects labelled, sterilized, and
tested for sterility.

The process of manufacturing a soft contact lens by lathe cutting.

1) The dry polymer is supplied as a rod or button.
2) A polymer button is placed on a lathe; the button spins and a diamond tool is advanced towards
the button to generate the lens back sur ace.
3) The button is released from the back surface lathe.
4) The button is mounted on a front surface lathe with adhesive wax; the button spins and a diamond
tool is advanced towards the button to generate the lens front surface.
5) The dry lens is removed from the lathe and the edges are polished.
 6) The lens is inspected at 17× magnification.
7) The dry lens is placed in saline to hydrate the lens, which swells to its final soft lens form.
8) The hydrated soft lens is inspected at 10× magnification.
9) The soft lens is inserted into a glass vial containing saline.
10) The glass vial is sealed and labelled.
11) The sealed glass vial containing the lens is sterilized in an autoclave.
12) The individual glass vials are dispatched.
Advantages of Lathe Cutting
 Lathe-cut lens are usually thicker (when compared with spincast lenses) and therefore, they are
relatively easier to handle.
 Lathe-cut lens has a better lens movement and centration when compared with spin-cast lens.
Disadvantages of Lathe Cutting
 Compared with cast molding and spincasting, it is time consuming and labour intensive. It takes
approximately 30 minutes to complete the manufacturing process, resulting in lens production
costs that are four to ten times more expensive than spincasting.
 Lathe cut lenses are difficult to reproduce, because each lens is individually made. To minimize
these variations most manufacturers use very simple designs, or introduce computerized
procedures for lens production.
 Lathe-cut lens usually have more than 1 base curve and therefore, it would require trial fitting in
order to determine the final base curve during trial fitting.

PRE-FITTING EXAMINATION
A routine preliminary examination should be done for each patient before fitting contact lenses. The
purpose of doing this is to:
1. Determine if the contact lenses are indicated or contraindicated.
2. Record important information before CL wear to establish a base line and assess changes if any.
The initial examination consists of following steps:
1. Assess reasons for wanting contact lenses and the motivation
2. Take detailed history of patient’s general condition, ocular condition, medication, and previous
vision correction, occupational and environmental factors.
3. Evaluate patients refractive error and best corrected vision
4. Examine the eye

1. Assess reasons for wanting contact lens and motivation.

2. Ocular examination: Perform a complete ocular examination to rule out any abnormality. This is
best done with a slit lamp. A torch with hand magnifier, or a 10 diopter lens case or a Burton lamp can
also be used.
These findings are necessary to indicate patient’s suitability and prepare baseline findings.
Assess the following structures: Rule out any abnormalities in the following:
 • Eyelid—like blephritis, meibomitis, trichaisis, chalazion, stye.
• Bulbar and limbal conjunctiva—pinguecula, pterigium,
• Palpebral conjunctiva- papillae, concretions, cystic growth
• Cornea—any opacity, keratopathy, keratoconus, neovascularization
• Iris- iritis, iridectomy
• Tears—stability, viscosity, tearproduction , break up time
• Sclera—thinning.

3. Take a detailed history of systemic conditions and contact lenses: Some general conditions, which
should be approached with caution while advising contact lenses, are
• Diabetes—are prone to infections and have delayed healing
• Pregnancy—prone to dryness and shift towards myopia, can continue lenses as long as they are
comfortable
• Allergies like asthma, hay fever –they are more prone to allergic reaction with solutions
• Arthritis—may have handling problems if deformities happen, or associated with dryness
• Sinusitis—more prone to red eyes and infections, more watering and discomfort.

4. Previous contact lens wearer: Careful history of his current contact lens and his satisfaction or
failure should be evaluated to avoid repetition of such problems.

5. Occupation and environment: Knowing patients occupation and needs, help to suggest the best lens
to the patient without dissatisfaction. Patients engaged in sports need very sharp vision and less
moving lenses like the soft lenses. Certain daily needs and fine work requirement are deciding factor
for the presbyopic patients. Patients in dusty environment may not adapt to RGP lenses and those in
chemical industry may have burning and stinging problems with soft lenses.

6. Refraction: The next and the basic step before considering contact lenses is the refraction. The
amount of the spherical and cylindrical correction is also the deciding factor for selecting the type of
the lens for the patient.
Refraction and best-corrected visual acuity should be recorded. Vertex distance compensation should
be made in case the powers are above +/–4.0 diopters. A Myope requires lesser power in contact
lenses and a hyperope needs higher power in the lenses. Details of power calculations will be
discussed later.

Ocular measurements
Corneal Curvature—Keratometry
Corneal curvature is the basic and the most important measurement needed before starting contact lens
fitting. The Keratometer measures only central 3 mm of the corneal curvature whereas the corneal
topographer gives the complete mapping of the cornea. However the Keratometer measurement is
sufficient in most of the fittings. During the measurements one should also make note of the corneal
irregularity if any.
The readings are taken in Diopters and then converted into millimeters. The readings also tell us about the
degree of corneal astigmatism.
The base curve of the contact lens is determined by the corneal curvature measurements.

Corneal Diameter – HVID

Cornea is a curved surface so an easy way to measure its diameter is by measuring the HVID – horizontal
visible iris diameter and the VVID – vertical visible iris diameter.
This measurement is taken by a simple millimeter scale , measuring the limbus to limbus size both across
the horizontal and vertical lengths.
The corneal diameter aids in determination of the Total diameter of the contact lens.

Pupil Size
The diameter of the pupil is measured by a simple millimeter scale both in standard room illumination
and low illumination. This aids in determining the optic zone size of the contact lens.

Palpebral Aperture and Lid Tension

The shape and size of Palpebral aperture varies in races specially the Asian versus Caucasian eyes.
Measurements are done by millimeter scale. The main purpose is to record so that changes can be noted
on follow-ups. There is no instrument to measure Lid tension.
It is a subjective method of measuring the tightness of the lid by asking the patient to look down and
pinching the lids from the eyelashes. Tight lids indicate greater displacement of the lens and may lead to
lid attachment fits. Lid tension can be classified as Tight, Loose and Medium.

Blink Rate
Normal blink rate (15 blinks per minute) is important for safe contact lens wear. Besides the recording of
normal blink rate, the quality of the blinks, whether complete or partial should also be noted. Incomplete
blinks will also lead to disrupted tear layer and corneal desiccation.

Tear Layer Assessment

Tear layer is an important aspect for estimating the suitability of the contact lens wear. The following tear
layer measurements should be undertaken
• Schirmer test , phenol red thread test
• Break-up time
• Tear prism height
• Lipid layer evaluation.

Schirmer Test
This test measures the volume of the tears. Special filter strips are bend over the notch and hooked over
the nasal lower lid margin. Patient is asked to blink normal during the measurements. The wet area of the
strip is measured after 5 minutes of insertion. Reading above 10 mm is taken as normal.

Phenol Red Thread Test

The test can be similarly done by using a 70 mm thread dipped in phenol red dye. The wet length is noted
as color change from yellow to red.

Break-up Time
This test measures the stability of the tear film. Fluorescein dye is instilled in the eye and patient is asked
to blink. The tear layer is then observed with the cobalt blue filter of the slit-lamp. The patient is now
advised to hold blink and the time taken for the first dry spot seen on the cornea is measured in seconds.
BUT - less than 10 seconds is suspicious of dry eye or unstable tear film.

Lipid Layer Evaluation

This is best done by the tearscope. Different colored fringes patterns are seen depending upon the
thickness of the tear layer. Thicker the layer means better tear stability and less evaporation. Thicker
layers also leads to lipid deposits problems.

Tear Prism Height

This is the height of the tear reservoir seen at the lower lid margin. Normal tear prism heights range from
0.1 to 0.3 mm. Height less than 0.1 mm signifies dry eye.

Patient’s Specific Needs

The selection of the lens may vary according to:
• Patient’s personal visual needs.
• Convenience and the duration for which the patient wants to wear lenses.
• Cost.

SUMMARY OF PRELIMINARY EXAMINATIONS

Recording History and Assessment of Indication/Contraindication

1. Indication for contact lens
2. Medical history any contraindication
3. Previous lens wear history
4. Motivation.

Ocular Examination
1. Visual acuity – uncorrected/ corrected
2. Refraction
3. Keratometry
4. Slit-lamp examination
5. HVID/VVID
6. Pupil size
7. Palpebral aperture
8. Lid tension
9. Tear break up time
10. Schirmer test
11. BUT
12. Suitability and type of lens.
 UNIT 2
SOFT CONTACT LENS FITTING
The fitting characteristic of soft lenses is a complex interaction of various ocular factors and definitely
needs proper understanding of the fitting techniques. One has to also understand that it is the fitter’s
responsibility if the patient develops complications due to improper fitting.
To start with let us understand the basic factors, which affect the fit of the lens on the eye.
1. Soft lens has a very low modulus of elasticity and so it drapes the cornea, due to which it is
generally seen that one universal base curve fits most of the corneas. Thin lenses are also more
flexible, so they move less than the thicker lenses.
2. Manufacturing method creates a difference in fitting. Identical curvatures but different methods
will cause different movement levels.
3. Fitting also depends upon the water content. Higher water content lenses are more flexible so
will move less than the low water content lens (provided the thickness is the same).
4. Keratometry readings are never a true predictor of the corneal shape and the Sag values of the
cornea. Thus patients with same K readings can have different lens parameters.
5. The movement of the lens fitting also depends upon the eyelid forces and position.
6. Tear film can also change the fitting characteristics. The lens tends to dehydrate on a dry eye and
so will move less.
7. Ionicity also alters fitting, hypertonic tears cause lens to dehydrate and thus move less.
Considering all of the above factor, it is sure that one can go wrong in predicting a perfect lens for the
patient on Empirical calculations. I suggest, one must evaluate the fitting on the trial lens method basis.
The Ideal Soft Contact Lens Fit
The overall goal of the soft lens fitting is to provide a lens, which gives adequate coverage, proper
centering and adequate movement so that the tear exchange and the debris is not accumulated. The lens
should not be tight on the eye so that it causes limbal compression, at the same time it should not be too
loose to that it is uncomfortable and causes unstable visual acuity.
The Fitting Steps
a) Do initial examination of the eye on the slit lamp biomicrosope
b) Determine the patient is suitable or not for soft lenses
c) Do accurate refraction. The spectacle cylinder should not be more than 0.75 diopters or well
within 4:1 ratio (spherical power : cylinder power)
d) Measure the corneal curvature by Keratometer. Although Keratometer is not a true predictor of the
soft lens base curve, as it has been studied that the fitting is dependent on the sag values and the
shape factor of the cornea, yet K readings cannot be ignored. If, available corneal topography is
more reliable.
e) Measure the HVID. The lens selected should be larger than the HVID.
f) Carry out other routine examinations like tear film assessment.
g) Select the lens type for the eye, Water content, material, thickness, modality, etc.
h) The selection of the trial lens:
The soft lens has the following basic parameters. The parameters of the trial lens, is selected on the
following criteria;
 Base curve
 Power
 Diameter
  Type of the lens.
Base Curve
Base curve is chosen on the basis of the keratometry. The modern designs may not actually predict the
base curve, yet this is the only logical way of selecting the first trial lens for the eye. Typical base curves
range from 8.1 to 9.1 mm (in 0.1 steps).
Steps for Calculations
1. Measure corneal curvature = convert in millimeters (refer to conversion chart)
2. Add 1 to the mean K reading
For example, Km = 43.0 @180 /43.50 @90
= 7.85 / 7.76
= 7.80
Add 1 to 7.80 = 8.80 mm
This is the base curve of the trial lens needed to start with.
a) This is best true for thick lenses, thin lenses need lesser addition to K reading
b) Depend upon the manufacturer’s guidelines in the fitting guide in trial lens selection.
c) Manufacturers nowadays usually do not supply curves in 0.1 increments. There may be 2 or 3 base
curves available. Select the lens closest to the required BC.
d) Where only 2 base curves are available, select the steeper BC for steep cornea and Flatter BC for flat
cornea.

Power/Back Vertex Power

The lens selected should have the power as close as possible to the spectacle power, or else maximum
within +- 4 diopter of the spectacle power. Disposable lenses can be fitted by empirical calculation of the
contact lens power based on the spectacle power.
Before fitting spherical soft lens one also needs to see that the spectacle cylinder is not more than 0.75 D.
More than this may need a toric lens.
There are 3 basic steps to calculate the expected power of the soft contact lens.
i. Transpose into minus cylinder form
ii. Spherical equivalent calculation—Half the amount of cylinder and add to the spherical power
(algebraically)
iii. Vertex distance calculation—If the spectacle prescription is more than 4.0 diopters. Power must
be adjusted for vertex distance. This can be read from the tables. Spectacle lenses are usually 13
mm from the cornea and contact lenses are supposed to be at virtually zero distance from the
cornea.
Some examples
Spectacle power Remarks Contact lens power
-2.50DS Same as spectacle Rx as less than 4D -2.50 DS
-2.50DS/-0.50DC@180 Half the cylinder and add to spherical -2.50+(-0.25) -2.75DS
More than 4, so refer bach vertex compensation
-8.00DS -7.25DS
chart.
 Spherical equivalent = -8.50DS
-8.00DS/-1.00DC@90 -7.75DS
Next compensate for vertex distance.
Selection of Power from Trial Sets
It is not possible to have all powers in all base curves. Unless, one stocks an inventory.
The basic trial set has the following powers in different base curves
1. –3.0 DS
2. –10.0 DS
3. +3.0 DS
4. +10.0 DS
The –3.0 lens works for all powers from 0 to –6.0 of spectacle prescription (within + – 4 diopters). The
-10.0 lens is suitable for anywhere between –6.0 to –14.0. A + 3.0 lens will work from 0 to +6.0 and the
+10.0 from +6.0 to +14.0.
After calculating the contact lens power from the spectacle prescription, select the trial lens with closest
power or within 4 diopters of spectacle lens power. In case of disposable lenses, calculate empirically and
select the lens from the inventory.

Diameter
The third basic parameter of soft lens is the diameter. The diameter is selected on the basis of the HVID
measurements. Add 2 mm to the HVID and the lens, diameter should be at least that much.
Typical soft lens diameters range from 13.0 to 14.5 mm (in 0.50 steps). It is logical to have an observation
of the cornea; normal corneal sizes can be fitted in this range. Smaller corneas may need smaller
diameters and some extra large ones may need 15 mm. These unusual lenses are usually custom designed
and are lathe cut designs. The basic rule is to cover the cornea adequately, so that there is no exposure of
the limbus on blinks leading to discomfort and epithelial staining.

Lens Thickness
The lenses can be classified as
1. Thick - 1 mm to 1.5 mm
2. Thin - 0.5 mm to 1 mm
3. Ultra thin - < 0.6 mm
The selection will depend upon the following pros and cons:
Thick Lenses
1. Thick lenses are supposed to mask cylinders better than the thin ones.
2. Thick lenses are easier to handle and can be suitable for those who are likely to have handling
problems.
3. Thick lenses reduce the oxygen transmissibility.
Thin Lenses
1. Have excellent transmissibility.
2. Drape the cornea so well that they do not mask astigmatism very well.
3. Have greater tendency to dehydrate and may cause corneal desiccation staining. This is more
likely in ultra thin lenses.
 4. They are not suitable for dry eyes.
Place the Trial Lens on the Eye
Although the patient with soft lenses will adapt immediately yet one must wait for some time before
evaluating the fit. This is because there is some amount of watering, and secondly the soft lens tends to
loose some water when on the eye, which may lead to parameter changes.
It has been studied that it is best to assess the soft lens fitting 5 minutes after insertion. Waiting for 15 to
20 minutes is not essential for the fitting assessment, but sometimes more time may be given to the
patients who want to psychologically adapt to them.

Evaluation of the Fit

Once trial lens has been fitted, its assessment has to be done. The following are the major criteria for
fitting assessment.
Patients Comfort Response
There will be some awareness of the lens, but there should not be discomfort. Sometimes the initial
discomfort is because of the differences of the lens solution pH and the tears. This resolves quickly

Comfort is an initial clue to the fit assessment.

1. Fairly comfortable initially Probably good fit
2. Uncomfortable Predicts loose fit (because it moves too much)
3. Very comfortable May be steep or tight (because it is immobile)

Corneal Coverage
The lens fit is evaluated best with the slit lamp, using a diffuse direct illumination.
With the eye in primary position, the lens should show full corneal coverage about 1 mm to 2 mm beyond
the limbus before, after and during the blink.
The coverage of the cornea is the predictor the diameter of the lens. If the coverage is more than 2 mm
means the lens diameter is too large or if the cornea is not fully covered means the lens diameter needs to
be increased. Corneal exposure may lead to corneal drying, staining and irritation.
1. Full corneal coverage (1 to 2 mm overlap) Ideal
2. Greater than 2 mm overlap Lens too large
3. Corneal exposure Lens too small

Lens Centration
The lens should be reasonably centered, extending equal distance beyond limbus in all directions. This
means that the optical center of the lens should fairly coincide with the center of the pupil. A decentered
lens can cause blurred vision and discomfort. Some decentration with adequate coverage all around is
acceptable. Decentered lens is not a true predictor of the tightness or looseness. It has to be judged by
other methods also to decide what alteration has to be done.
1. Centered in all positions of gaze - Ideal and required
2. Decentered with corneal exposure in any position of gaze - Lens may be tight or loose, diameter may
be small. A thinner lens can be tried.

Lens Movement
The movement of the lens is essential for proper tear exchange and removal of debris. Inadequate
movement will lead to inflammation, edema and red eye (CLARE). It is the most important evaluation
technique.
The movement of the lens is a judgment of an individual. The patient is asked to look straight in the
primary gaze and asked to blink normally. Estimate the movement of the lens while observing with
diffuse light and high magnification the amount of the movement with each blink. The best way is to
learn from experience initially by trying different base curve lenses on an individual and estimating the
steepness and flatness on the basis of the movement.
The movement of the lens depends upon the type of the lens, its design and thickness. One must follow
manufacturers guidelines. Thick lathe cut lenses may need a movement of 1 to 2 mm, but modern thin
design lenses are required to move by 0.2 mm to 0.1 mm This small movement of the lens is at times
difficult to assess. The push up test is always performed with this to finally decide if the lens is steep or
flat.
0.2mm to 0.4mm movement Ideal movement For thin lenses
> 0.2mm movement Tight lens For thin lenses
< 0.4mm movement Loose lens For thin lenses
1mm to 2mm movement Ideal For thick lenses

Push-up Test
Push-up test is a valuable aid in determining the lens fitting relationship.
The patient looks straight and the examiner pushes the lens up vertically, through pressure on the lower
lid.
The examiner will then estimate the relative ease with which the lens moves up and the smoothness by
which it recenters.
A 100% tight lens will resist any movement on push and will be difficult to displace. A loose fitting lens
will slide off easily but will be sluggish to return or may not recenter even.
An ideal fitting lens will displace easily and return smoothly. The tightness experienced on push-up test
should be more than 50%. This again is a subjective judgment.
Easy displacement Smooth recovery and recentration Optimum fit
Resistance to displacement May not recenter Tight fit
Easy displacement Erratic recovery Loose fit

Lens LAG on Upgaze

The patient is asked to look up, the lens will move down slightly. This is called Lag. The amount of lag
depends upon the fitting relationship.
An optimum fit shows a lag of 1 to 1.5 mm. Less than this indicates steep fit more than this indicates a
flat fit.

Edge Alignment
The edge of the lens should be observed with reference to the conjunctiva. If the edge is sliding smoothly
and aligning with the conjunctiva it is a desired result. If the lens edge indents on the cornea the lens is
tight. If it stands off the lens is loose.

Other Responses for Estimation of Fitting Relationship

These are some more indicators in fitting assessment. Slight steepness and looseness cannot be predicted
by these tests. Gross fitting errors can be estimated by them.
Vision Before and After Blink
If the lens fit is ideal the vision will remain clear before and after blink. Variation of vision with blink
indicates steep or flat fit. If the vision clears with blink it is a steep fit, if it blurs after blink it is a flat fit.
Keratometry and retinoscopy with the lens on the eye can also be performed. The patient is asked to blink
and the clarity of the mires soon after blink is observed. If it gets clear with blink it is a steep lens, if it
gets blurred or distorted soon after blink it is a loose lens.

Alter the lens if ideal fit is not achieved

If the first trial lens does not show adequate fit, find and refit another appropriate lens.
There are 3 basic parameters on which the lens fitting depends.
The fitting relationship can be changed on this basis:
1. Base curve
2. Diameter
3. Thickness
Increasing the base curve flattens the lens fit and decreasing it steepens it. If 8.3 BC is behaving steep,
depending upon the steepness, decide the next flatter BC like 8.4 or 8.5
Increasing the diameter increases the Sag so it tightens it. The diameter of the lens should be also be
increased or decreased depending on the corneal coverage. Suppose a 14.5 mm diameter lens behaves
tight reducing the diameter to 14.0 or 13.5 mm will flatten the fit.
Increasing the thickness of the lens fit increases the movement, hence loosens the fit.
Altering the base curve and the diameter - without changing the fitting relationship.
The rule of thumb is
0.3 mm change in the base curve = 0.5 mm of change in diameter
Let us consider an example: an 8.3 mm BC , 13.5 mm lens will give the same fitting relationship
as an 8.6 mm BC and 14.0 mm lens.
Over Refraction
It is advisable to refract over the diagnostic lens to confirm the power of the lens and to rule out any
residual astigmatism. The lens will also confirm the final visual acuity that can be achieved by the soft
lens.
Do retinoscopy over the trial lens. Take patients acceptance by which it achieves the best visual acuity.
Calculate the final lens power by algebraically adding the power of the diagnostic lens and the additional
power needed.
Note
a. The additional power needed should be always less than 4 diopters. (Else the back vertex calculations
of the added lens will further have to be calculated)
b. The final lens power in the spherical lens fitting is a spherical power. So the additional lens power
should always be spherical power. If there is significant cylindrical acceptance over the diagnostic
lens and the vision is not acceptable by spherical equivalent then fit a toric lens.
Example:
Power of trial contact lens on the eye = –3.00 Dsph
Over refraction = +0.50 Dsph
Final lens power to be ordered = +2.50 Dsph

Final Order of the Soft Contact Lens

 Base curve
 Power
 Diameter
 Water content
 Tint
 Material
 Manufacturer

SUMMARY
1. Measure
 Keratometry
 HVID
2. Determine contact lens parameters
 Base curve
 Diameter
 Power
3. Select the lens type
4. Assess fitting after lens settles on the eye
 Coverage
 Centration
 Movement
 Comfort
  Push up test
 Lag
5. Assess vision
 Over refraction
DISPOSABLE CONTACT LENS
The disposable contact lens is the result of the development of molding based manufacturing methods that
make possible the production of uniform lenses at low cost. Clinically, they are called ‘‘disposable’’
because the contact lens is made of a hydrogel (soft lens) material that can be replaced after 1day, 1week,
or 2 weeks or of a silicone hydrogel developed for extended wear and discarded monthly. Hydrogel lenses
exchanged at intervals of every 3 or 6 months are often referred to as ‘‘planned or frequent replacement.’’
Literally, all contact lenses are planned-replacement or disposable. The eye care practitioner and the
patient simply choose the optimum interval at which to replace them.

Indications for disposable contact lens

Disposable contact lenses are indicated for the correction of myopia, hyperopia, astigmatism, and
presbyopia, as well as for cosmetic purposes. They are routinely prescribed for:
 Allergic individuals with sensitivity to chemical lens care system products
 Individuals who wish to use lenses on an extended wear basis because of difficulty with
maintenance, the type of work they do, or convenience
 Patients who frequently lose contact lenses or need spare lenses
 Patients who play contact sports
 Wearers who are exposed to pollutants
 Individuals who suffer from giant papillary conjunctivitis (GPC)
 Individuals with lacrimal deficiency or who form excessive deposits on the contact lenses
 UNIT 3

SOFT TORIC CONTACT LENS FITTING

Soft toric contact lens fitting for astigmatic eyes is supposed to be a specialty fitting, whereas the modern
designs and fitting guidelines have simplified so much that they are as easy as a spherical soft lens fitting.
An additional understanding of the design, its axis and power calculation is needed to fit an astigmatic
eye.
Astigmatic correction upto 4 .0 diopters can be achieved with rigid spherical lenses. With spherical soft
lenses spectacle cylinder is acceptable upto 0.75 diopter can only be corrected. The incidence of
astigmatism surveys that 16% of prescriptions have more than 1.0 diopter of astigmatism, which increases
to 30% with 0.75D or more of astigmatism.
With the increasing demand for comfort and better visual acuity soft toric lenses are getting popular now.
We have various options to correct astigmatic eyes like
1. Spherical RGP
2. Toric RGP (not available in India)
3. Soft toric lenses.
Indications for Prescribing Soft Toric Contact Lens
1. When the best sphere (spherical equivalent) does not give a satisfactory visual acuity.
2. When there is residual astigmatism more than 0.75 diopters with spherical soft lenses. This
residual cylinder causes discomfort/asthenopia to the wearer.
3. When the rigid gas permeable lens is uncomfortable.
4. When the sphere to cylinder ratio is less than 4:1.

Spectacle refraction Ratio sph : cyl Toric cl indicated?

– 3.0 Ds / – 0.75 Dc 3 : 0.75 Not necessary
– 8.0 Ds /– 1.50 Dc 4 : 0.75 Not necessary
– 0.50 Ds /– 1.0 Dc 4:8 Yes
– 12 .0 /– 2.0 Dc 4 : 0.75 Not necessary

5. It depends on patients’ visual needs. Some may be satisfied with the visual acuity, which may not
reach the 6/6 target with spherical lenses, and some may be very sensitive about the sharpness of
visual acuity.
6. Uncorrected astigmatism can be tolerated in non-dominant eye but not in the dominant eye.
7. A spherical refraction with corneal astigmatism does not need a toric contact lens.
Since, soft toric lenses available in our country this chapter will discuss the fitting philosophies of soft
toric lenses only.
A spherical soft lens has only one curvature whereas a toric lens has two different radii of curvature in
two principal meridians. In case of toric spectacle lenses we order the cylindrical axis and the fitter fits it
in the spectacles according to the axis specified. This does not happen in the eye. The lens rotates and
behaves different in every eye. This is due to different anatomy and lid positions of an individual eye.
So, all soft toric lenses have a stabilization technique to prevent axis mislocation on the eye.
The lids and the lid forces hold the contact lens in the palpebral space. Lens movement will attempt to
move the lens in the same direction as itself. In case of toric lens, the rotational movement is made stable
in the vertical axis.
Good vision with any kind of toric lens needs stable cylinder axis location.
The soft toric lenses stabilizing mechanisms are:
 Prism ballast
 Truncation
 Peri-ballast
 Double slab-off
 Reverse prism
Prism Ballast
In this technique 1 to 1.5 D base down prism is incorporated near the inferior periphery of a round lens.
The prism acts as a weight and prevents rotation. The stability is thus provided by the difference in
thickness. Based on the watermelon seed principle the thin edge of the round lens lies under the upper lid
and the thicker edge rests over the lower lid. This is the simplest and most common adapted technique for
stabilization of a toric lens.
This design creates some discomfort along the lower lid margin due to thick edge. This thick edge also
reduces the oxygen transmissibility at the lower thick edge of the lens.
Truncation
In this technique the lower portion of the lens is cut horizontally, so that the lens rests on the lower lid and
is stabilized. These truncated edges may be source of discomfort. This technique is also not always
successful in practice as truncation alters the thickness profiles and differentials. It is also difficult to
manufacture and finish.
Peri-ballast
This technique utilizes the minus carrier design at the edge. This is then converted to create a prism base
down effect and uses the thickness differences as stabilizing component. This technique like prism ballast
may cause discomfort at the lower lid and reduce oxygen transmissibility at the thicker edge.
Double Slab-off
Thin zones are first created at the edges. Due to lid interaction and thickness profile the lenses are
stabilized. The thin zones upper and lower interact with the lids especially the upper lid, to position and
stabilize the lens on the eye. This lens has better comfort due to reduced lens thickness. This design may
not work in patients with loose lids.
Reverse Prism Designs
This design incorporates two prisms one base up and other base down prism. Chamfering is done at the
prism base to cut off the inferior edge horizontally which reduces the discomfort and creates a prism less
optic zone.
It is an advancement of the prism ballast design.
Based on the surface where the cylindrical power is the toric lens is classified below.
Types of Toric Lenses
  Back toric
 Front toric
 Bitoric
Front Surface Toric
When the front surface has two radii of curvature and the back surface is spherical. This corrects total
refractive astigmatism.
Back Surface Toric
The (base curve) posterior curve has two different radii of curvature at two principal meridians and the
front surface is spherical. These lenses will correct the corneal astigmatism.
Bitoric
Both anterior and posterior surfaces have two different radii of curvature at two principal meridians.
These lenses also correct the total refractive astigmatism. These lenses are also uncommon.
Axis Marks on Toric Soft Lens
Some form of reference mark is needed on the toric lens to assess the rotation. Different manufacturers
have different markings. They may be permanent (usually) a laser or mechanical engraving or a
temporary one with an ink or dye. They are either a single or 3 marks with a specific separation angle at
the 6 o’clock or horizontal axis. One must refer to manufacturer’s guidelines before estimating rotation.

Fitting Guidelines
Step 1
Perform refraction. (minus cylinder form). Be very accurate.
Step 2
Do keratometry.
Step 3
Estimate the total astigmatism.
Total astigmatism = corneal astigmatism + internal astigmatism
Step 4
Selection of the trial lens : Select the design on the basis of the type of astigmatism.
Base Curve and Diameter
Select the base curve as per the keratometry and the diameter on the basis of HVID. The selection is made
the same way as in the spherical soft lens.
Power and Axis
The trial set consists of two axis 180 and 90 degrees in the base curves available. Select the lens, the axis
of the cylinder, which is closest to spectacle prescription. If the minus cylinder axis is near 180 degrees
select the 180 degree reference lens, and if the minus cylinder axis is near 90 degrees select the 90 degree
axis reference trial lens.
The power of the trial lens is immaterial. The purpose of the trial lens is to calculate the axis rotation.
The power of the contact lens is calculated from the spectacle prescription. Over refraction is not
performed in finalizing the power of the lens.
Disposable Toric Contact Lens
The method is to order a trial lens based on empirical calculations from the spectacle prescription and
keratometry. The final orders are made with adjustments, if needed, on this lens.
Step 5
Insert the trial lens and wait for 15 to 20 minutes.
Step 6
Evaluate physical fit and measurement of lens rotation. Physical fit – finalize the base curve first.
Finalize the base curve first the same way as spherical soft lens.
Calculate the rotation as explained in the next step, on the base curve and diameter, which will be ordered
in the final. Do not calculate the rotation if any unless the BC and OD are finalized.
Measurement of Lens Rotation
The rule is based on the principle of LARS or CAAS To identify the lens rotation, observe the markings
on the lens. (Depends on the manufacturer)
Suppose, the trial lens has 3 orientation markings at 5, 6, 7 o’ clock position of the lens. The separation of
each marking is 30 degrees (one clock hour is equal to 30 degrees). The position of the lens if shifts such
that the 5 o’clock marking shifts to 6 o’clock position the lens is supposed to have rotated by 30 degrees.
If the lens rotates to the practitioner right (anticlockwise) subtract that many degrees from the axis of the
spectacle prescription. If it rotates to practitioner left (clockwise) add that many degrees of rotation to the
spectacle prescription.

L A R S
Left Add Right Subtract

Note
 The final lens will show the same degree of rotation when placed on the same eye.
Methods of measurement of rotation
i. Narrow slit beam of the slit-lamp
ii. ii. Cylinder marking in the trial frame
iii. Protractor scale of the eye piece graticule
iv. Estimation from markings position.
The axis rotation gives the practitioner the information needed to order the next lens. The rotation shows
that how far the axis of the cylinder will be mislocated when the final lens will be placed on the eye.
Step 7
Calculate the power from the spherical and the cylindrical from the spectacle prescription order power
based on these calculation.
This calculation is done in following steps:
1. Writing the spectacle prescription in the cross cylinder form (at 2 principal meridians)
2. Then compensate for the back vertex
3. Rewrite in sphero cylinder form.
Suppose the spectacle power is
–2.0 Dsph / –3.0 cyl × 180

Rewrite in spherocylinder form (compensating BVP)= –2.0Dsph / –2.67Dcyl × 180

Hence the power of the toric CL ordered is –2.0 Ds / –2.67 Dc × 180. (Take the cylinder value closest to
the one available).
Taking one more example
–6.0 Dsph / –2.0 Dcyl × 90

Step 8
Final order
 Base curve
 Power and axis
 Diameter
 Lens type (design)

Insertion, recentring and Removal of soft contact lenses

1. Insertion.
 Stand to the side of the patient.
 Place the lens on the tip of a dry index finger. Use the hand which would be most convenient for
lens insertion. Inspect the lens to ensure that it is oriented correctly, i.e. not inside out, that it is
clean and free of debris and not damaged.
 Instruct the patient to fixate at an object in the straight ahead position.
 Pull the lower lid margin down with the middle finger of the hand holding the lens. Now instruct
the patient to look down. Lift the upper lid with the thumb of the other hand while resting this
hand on the patient’s forehead.
  Now ask the patient to look straight ahead again and gently move the soft lens towards the cornea
until contact is made. Because of capillary attraction the lens should adhere to the ocular surface.
 Slowly release the lower lid and then the upper lid so that the lens is not displaced by the force of
the upper lid. Several attempts may be needed before mastery of the technique is achieved.
 Minimal discomfort should be experienced because soft lenses are flexible and large. If
discomfort is experienced it may mean that the lens is inside out or that debris is trapped under the
lens which is likely to result in hyperlacrimation.
2. Locating and Recentring soft lenses.
 If the lens is displaced from the cornea, locate the lens by retracting the lids from the bulbar
conjunctiva.
 Soft lenses are more likely to be superiorly displaced and occasionally the lens may be folded as
well. To expose the superior bulbar conjunctiva, ask the patient to look down and retract the
superior lid.
 To search for the lens under the lower lid, ask the patient to look up while retracting the lower lid.
 If the lens is displaced, touch the centre of the lens with the tip of the index finger while retracting
the lid and gently slide it over the cornea.
 If the lens is folded and displaced, remove the lens, rinse it and then ensure that it is the right way
around before it is reinserted.
 Because soft lenses are large it may be possible to recentre the lens (particularly if it is laterally
displaced) by merely asking the patient to look in the direction of the lens.
3. Removal of soft lenses.
1. Pinching Technique:
 Ensure that the lens is centred on the cornea before attempting to remove it.
 The patient is asked to look nasally while the practitioner retracts the bottom lid with the third
finger of the one hand and the top lid is retracted with the thumb of the other hand.
 Touch the lens with the index finger of the of the hand that is retracting the bottom lid and slide
the lens on to the temporal sclera.
 While still holding the lids apart, pinch the lens gently with the thumb and index finger while
ensuring the fingernails do not touch the lens
 Remove the lens.

2. Alternate technique:
 Ask the patient to look up. Then retract the lower lid with the middle finger and slide the lens
down with the index finger. As soon as the lens is halfway off the cornea, pinch the lens with the
thumb and index finger.

3. Scissors technique:
 The patient looks straight ahead.
 The upper and lower lids are held apart at the lid margins midway between the inner and outer
canthi.
 Gently stretch the lids. This will squeeze the lens out of the eye.

4. Place the lens in the palm of the hand. Place a few drops of cleaning solution on the lens and rub the
lens with the index finger for about 10 seconds . Repeat this procedure twice again using saline
solution. Put the lens back into the vial with fresh disinfecting solution. Close the vial with a rubber
 stopper and crimp the stopper and vial. If saline solution is used, the vial should be thermally
disinfected.

DO’S AND DON’TS OF LENS CARE

Besides the instructions, of care and maintenance and insertion removal the patient should always be
added some basic Do’s and Don’ts, which will reinforce proper compliance. These also form a part of
queries, which usually appear in patients mind during lens wear. These should be written and discussed
with each contact lens wearer to avoid complications.
Reinforce these Do’s
1. Always wash hands, before handling contact lenses.
2. Follow the recommended wearing schedule.
3. Keep the lens case clean and replace as advised.
4. Handle lenses over clean table. Washbasins are risky; lenses can be lost down the drain.
5. Clean and disinfect lenses daily after use.
6. Carry a lens case filled with solution with you while going out of the house.
7. Remove lenses immediately if redness, watering, or irritation start. Consult your practitioner
immediately.
8. Wear goggles when moving out in a dusty environment.
9. Follow instructions regarding cosmetics usage with contact lenses.
10. Read all the instructions carefully before starting wear.
Warn these Don’ts
1. Do not sleep with the lenses on the eye, unless recommended.
2. Always replace the soaking solution every night. Don’t add over the existing solution.
3. Saline solution if used for rinsing should not be home made.
4. If unpreserved saline is used for rinsing, it should be discarded after every use.
5. Soft lenses cannot tolerate most of the RGP solutions. Read instructions always properly before
buying solutions over the counters.
6. Do not change the brands of solutions unless recommended by the practitioner.
7. Buy smaller bottles as far as possible and discard after expiry of opening.
8. Do not touch, the tip of the solution bottle with hands, this might contaminate them.
9. High water content lenses should not be heat disinfected.
10. Some tinted lenses may lose their tint intensity with peroxide systems. Avoid them.
11. Lenses unused for long time should be disinfected always before reuse.
12. Cracked or chipped lens should never be worn.
Do not rub your eyes vigorously with lens on the eye.
 UNIT 4
CONTACT LENS CARE SYSTEM
When the lens is received from the manufacturer it is sterile, so where does the infection come from.
Clearly, most of the complications with contact lens are because of the poor compliance and improper
usage of the lens care systems. It is the responsibility of the practitioner to understand first and then
explain the proper usage of each care system.
Care systems or solutions used for contact lenses are ample in the market today. The purpose of this
chapter is to understand the function of each constituent.
The Purpose and Objective of a Lens Care System
 To maintain comfort
 Provide good vision
 Maintain eye health
 Maintain lens hydration and parameters stability
With every wear the lens attracts proteins, lipids, mucins, minerals from the eye, and cosmetics,
microorganisms and contaminants from external sources like hands.
These accumulate on the lens and form a coating called the biofilm. The lens undergoes changes in
parameters due to this, leading to complications like decreased comfort, decreased vision, reduced
wearing time, inflammation and infections.
The purpose of the lens care is thus to make the lens wear safe for the eye.
A Typical Lens Care System
Cleaning
It removes microorganisms and loose debris and prepares lens for disinfection.
Rinsing
Removes the cleaner and debris after cleaning.
Disinfection
Kills microorganisms, which may remain on the lens.
Enzymatic Cleaning
Removes firmly attached proteins from lens surface.
Lubricating
Rewet the lens surface while the lens is being worn.
Chemical Properties of Care Products
All lens care systems should:
 Adequately perform cleaning, rinsing and disinfection
 Be nontoxic and harmless to ocular tissues
 Be compatible with lenses and cause no changes in parameters
 Be simple to use
  Be affordable.
THE LENS CARE SOLUTIONS HAVE FOLLOWING PROPERTIES AND INGREDIENTS
Tonicity—0.9% NaCl
The standard of tonicity is 0.9% NaCl (sodium chloride). Solutions are formulated to be isotonic in order
to maintain the water balance of the contact lenses and the ocular tissues.
Sodium chloride—NaCl is the primary tonicity agent used in lens care formulations.
Degree of Acidity/Basicity
pH—6.6 to 7.8 Comfort Range
The average pH of human tears is from 7.0 to 7.4. Solutions that are outside the eye’s comfort range of
6.6 to 7.8 will cause discomfort, usually burning and stinging when put in the eye.
Small quantities of HCl (hydrochloric acid) and NaOH (sodium hydroxide) are common ingredients
needed to adjust the pH.
Buffering Agent—Maintain pH
Atmospheric carbon dioxide can enter into the open bottles and dissolve in the solution to make carbonic
acid. This lowers the pH. Buffers are thus added in the solutions to maintain the pH to comfort levels of
7.0 to 7.4, e.g. borate, phosphate or citrate.
Viscosity—Increase Contact
Viscosity agents are added to the solutions for greater contact with surface, e.g. polyvinyl alcohol, methyl
cellulose, hydroxyethyl cellulose, sodium hyaluranate.
Antimicrobial Activity
Solutions have a preservative and a disinfectant.
Preservatives: Resist or prevent microbial growth in solution once opened.
Disinfectants: Control growth of microorganisms in lens care solutions and eliminate harmful organisms
from the contact lens.
Safety vs Efficacy of Preservatives and Disinfectants.
All solutions must be strong enough to kill microorganisms but at the same time mild enough to harm
ocular tissue.
Commonly used Antimicrobial Agents in Contact Lens Solutions
1. Biguanides: For example, polyaminopropyl biguanide, polyhexidine. They are chemically similar to
chlorhexidine and have large molecules, which are not absorbed by lens material. They are effective
against bacteria but not so much against fungi. They are used in low concentrations (0.00005 to
0.0001%).
2. Polyquad: Concentration 0.001 - 0.005%. They are also large molecule, which are not absorbed by
lens. They are less irritating to the eye and can be used both as preservative and disinfectant.
3. Hydrogen peroxide: It is cidal in low conc. 50 -60 ppm. High concentrations of 3% very effective
but need to be neutralized before insertion of the lens into the eye.
4. Sorbic acid: It is a moderately effective preservative. It has good action at low pH also. It may react
with proteins on the lens and cause discoloration.
5. Benzalkonium chloride: It has detergent action and causes disruption of cell membrane. It is used in
certain eye drops and RGP solutions. It binds to SOFT lens, and cause severe toxic reactions. So no
BAK preservative solutions should be used with soft lenses.
6. Chlorhexidine: It has cidal action and can cause toxic reactions. It is both used as preservative and
disinfectant. It is very effective against fungi, especially when combined with thiomersal.
7. EDTA: It is a chelating agent that is it binds with metal ions needed for growth. It has no cidal
activity of own.
8. Quaternary ammonium: Same action as BAK but has larger molecules so less toxic.
9. Thiomersal: It is mercury based, and has cidal action against bacteria and fungi. It is common to see
hypersensitivity reactions with thiomersal. It is used in 0.001% as preservative 0.005% as disinfectant.

Surfactants
It is used in cleaners. They bind with loose debris, deposits and microorganisms and form micelles -
which are removed easily with rinsing, e.g. poloxamer, isopropyl alcohol, tyloxapol, sodium laurel
sulphate.
Stabilizers
They prevent dissociation or degradation of chemical formulation, e.g. phophonic acid, sodium nitrate,
sodium stannate.

LENS CARE REGIME STEPS

Cleaning
This process should be done daily. Proper cleaning removes 90% of organisms, so the time the lens
reaches the disinfection step there is a significant reduction in microbial contamination.
Cleaners mostly contain—surfactant, viscosity agent, chelating agent, buffer and preservative.
There are some specialty cleaning agents like polymeric beads which have abrasive cleaning agent or
isopropyl alcohol for dissolving lipids.
Enzymatic Cleaners
They also form a part of cleaners by breaking down of proteins. This step is done mostly weekly but
depends on the condition of the eye and the deposition. Frequent replacement program lenses may not
need this step. It is important to thoroughly rinse the traces of enzyme cleaners from the lenses else they
may cause burning and stinging. The lenses tonicity and pH also may have to be re-equilibrated after this
step.
Enzymatic cleaners are available in tablet form and contain either of the following compounds:
1. Papain—it is an enzyme derived from papaya, may cause ocular irritation, has an unpleasant
sulphur odor, is incompatible with some hydrogen peroxide systems and is not so popular
2. Pancreatin—is derived from pig pancreas and is effective against protein, lipid and mucin
deposit.
 3. Subtilisin—from bacterial fermentation of bacillus lichniformis. It is compatible with all
chemical, thermal and peroxide system of disinfection.
Protein removal has following advantages:
 Regular removal of adherent protein film and deposits
 Increase lens life
 Maintain comfort and vision
 Reduce ocular complications
Emphasis should still be on regular replacement of hydrogels.
Procedure
Clean the lens, prior to enzyme treatment. Soak one tablet of enzyme in 5 ml of soaking solution. Soak
the lens in this enzyme solution from 15 mins to 4 hrs (follow manufacturer guidelines). Remove lens and
clean very well again. Re-soaking, in fresh solution, may be needed in some type of tablets. The enzyme
solution is very irritating to the eye and special care should be taken to clean the lens very well before
insertion.
RINSING AGENTS
Saline solutions are the rinsing agents in contact lens care solutions. Their purpose is to rinse to remove
cleaner and loose debris. Saline is usually preserved with preservatives so that it does not get
contaminated after opening. Unpreserved saline are also used in patients who are sensitive to
preservatives. In this case single dose disposable saline units should be used. Unpreserved unit doses are
used to avoid toxic reactions.
It has been seen that home made saline can also be prepared. It should be discouraged as home made
saline is a great risk and increase the incidence of infections by many folds.
DISINFECTION
Disinfection is done after each wear. It protects the eye from infection. With every wear the lens gets
contaminated and the common sources of contamination are from hands, cosmetics, tap water, soiled
cases.
There are two main methods of disinfection
 Heat
 Chemical
Heat or Thermal Disinfection
It requires a temperature of 80 degrees for 10 min, followed by cooling period.
Heat disinfection has:
Advantages
Effective against bacteria, fungi, virus and amoeba
 Short disinfection time
 Can be preservative free
Disadvantages
  Decrease lens life
 Degrades polymer
 Not suited for > 45% water content
Due to its disadvantages the thermal disinfection method is not encouraged these days.
Chemical Sterilization
This method utilizes the property of preservatives and disinfectants to sterilize the lens. Soaking the lens
in the soaking solution for an appropriate time sterilizes the lenses. The efficacy depends on preservative
type, concentration and the soaking time. Soaking solutions should be discarded after every use. They
lose their potency with reuse.
Advantages
 Convenient
 Inexpensive
 Is compatible with most of the modern lens materials
 Most popular method recommended.
Disadvantages
 Preservatives can bind to lens materials and deposits
 Can irritate the cornea
 Patients can develop toxicity reactions
 Certain disinfectants have limited antimicrobial activity.
Oxidative Chemical Disinfection— Hydrogen Peroxide
Hydrogen peroxide is a very effective disinfectant for a wide range of bacteria and viruses for a relatively
short exposure of time (10 minutes approx).
An oxidative reaction occurs whereby the hydrogen peroxide molecule breaks down into free radical,
which disrupts the cell wall of the microorganisms. This free radical breaks into water and oxygen
further.

H2O2 → HOOH → H2O + O2

(Free radical)
0.005 to 0.006% is effective as preservative and 3% is effective disinfectant. This peroxide needs to be
neutralized before the lens is placed on the eye.
Hydrogen peroxide disinfection system has following advantages:
 It can penetrate deep into pores of lens matrix
 Has very good disinfecting property
 Does not need preservative as has acts as preservative on its own
 It has some cleaning action by breaking down protein and lipid bonds
 It is nontoxic if properly neutralized.
It has following disadvantages:
• It may cause ocular toxicity if is not neutralized properly
• It is expensive
 • More complex to use
• May effect parameters of FDA group IV lenses.
Neutralization compounds used in peroxide system to convert H2O2 into water and oxygen.
1. Catalytic disk of platinum
2. Sodium pyruvate and sodium thiosulphate
3. Catalase.
Based on this the peroxide systems are classified into one step or two step systems.
One step peroxide
 is convenien
 pH is close to 6.5
 has inflexible neutralization time
 can be used with protein tabs.
Two step peroxide
 has short neutralization time
 the pH is acidic 3.5
 does have flexible disinfection time.
Lubricating or Rewetting Drops
Very often contact lens wearing patients complain of dryness. This is usually because of wind, dust, low
humidity, heat or even marginal dry eye. Rewetting or lubricating drops need to be added to improve the
wettability and prevent the lens from drying in the eye. It relieves the symptoms associated with dryness
like discomfort reduced wearing time and irritation.
Rewetting drops can be used with the lenses on the eye. Certain artificial eye substitutes or tear
supplement drops can also be used, but the preservative in them can bind with the soft lens material and
cause problems. So it is safe to use the recommended lubricating drops with the lens on the eye.
Efficacy
The efficacy of disinfection against bacteria is –
Heat, 3% H2O2, thiomersal 0.002% (4 hrs), dymed 0.005% (4 hrs) polyquad 0.001% (4 hrs).
For fungi and acanthamoeba the effective methods are— Heat, H2O2, thiomersal. 002% (4 hrs). Dymed,
polyquad, are ineffective against fungi and acanthamoeba.

Compliance
Compliance to maintenance is a very important step to avoid all problems. One should keep check of
compliance regularly.
The compliance expected from patients for safe healthy wear is in the field of:
1. Care regimen instructions
2. Lens wearing schedules
3. Follow-up visit schedule
4. Lens replacement schedule
Multipurpose Solutions
To improve compliance, multipurpose solutions are available and popular these days. They are care
systems that perform more than one function. Cleaning, rinsing and disinfection are commonly achieved
with one solution only. Some solutions may also offer protein removal and enhanced lubrication also.

OVERVIEW OF LENS CARE SYSTEMS

 Cleaning
 Rinsing
 Disinfection
Optional Lens Care Systems
 Enzyme cleaning
Lubricating.

FOLLOW UP VISIT EXAMINATION

As a responsible practitioner, one must not neglect the patient after dispensing. Unlike spectacles, the lens
is in contact with the eye and the eye can respond negatively. Several times the patient may not be aware
of the warning signs and symptoms which may gradually lead to major problems. These can be very
comfortably taken care of in the beginning. It is also studied that most of the problems arising due to
lenses is because of poor compliance on behalf of the patient. During the follow up visit one can reinforce
and rectify that, thus preventing complications and drop outs.
The After Care Routine
After care, should include both subjective and objective assessment of the lens. Review the information
recorded at previous visits. The record file should always be maintained and further information recorded
on follow-ups.
Subjective Assessment
Patient Discussion
Start with history—ask questions. Be specific and open. Encourage patient to ask questions during the
discussion. Recheck the compliance. Before the examination, make a note of the following; these will
support you in recommending corrective actions.

 Lens age: Every lens has a life. Patients may not be sure of the replacement. Some of the
complications may be associated with the aging lens.
 Wearing habits and time: Ask- How many hours during the day does one wear lens? How many
days during the week? Does one sleep with lenses on?
If the patient is comfortable wearing lenses during full waking hours, hints that the lens fitting is
reasonably good. If the patient admits that he does occasionally sleep with lenses, indicates a thorough
examination and need for improved compliance.
 Review lens care system: Ask patient to demonstrate. Ask the patient to insert and remove the lens in
front of you. Observe his habits and compliance then. Check that he does wash hands; the nails are
trimmed and use solutions in proper way and steps.
 Presence of problems: Patients may have specific symptoms or at times may neglect some minor
complaints are warning signs Ask questions to arrive at conclusions.
 Reduced and blurred vision: Constant or fluctuating, or any specific circumstances when
happens
 Discomfort: Foreign body sensation, burning, stinging, dryness, grittiness, itching immediate
onset (soon after insertion) or Delayed onset (after may be an hour of wear), with or without
lenses.
 Environment and occupation: Air-conditioned office, and computer usage, may lead to
dryness.
 Systemic problems: Ask if the patient has any systemic problem, which has any correlation
with lens wear. Confirm about any intake of drugs and medications.
Objective Assessment
Check up should be done with lenses on and then after the lenses are removed. The assessment should be
done with the patient attending the clinic with the lens worn for at least 4 hours before the check up. This
should be explained on the dispensing visit itself. Many of the delayed problems can be identified only
after some hours of the wear. If the patient comes for the check up and inserts lenses there it self, some
signs may be missed out.
The slit-lamp is the key instrument, which will allow accurate objective assessment.
To start with check with lenses on:
 Visual Acuity - Record distance and near visual acuity, monocular and binocular. Any deficiency
calls for power adjustments. If the patient complains of blurred visual acuity after some hours of wear,
rule out corneal edema.
 Retinoscopy Over the Lenses - This is the most important technique, after all lens, is a vision
correcting device. The refraction over the lens will guide you if there is any deficiency of power, any
over correction, and residual astigmatism. It also hints you about the fitting (clear reflex before and
after blink). The reflex through the lens will show deposits and the dirty lens, which calls for
replacement. If the optic zone is cutting through the pupil can also be seen now. One can also check if
the lenses are switched.
 Slit-lamp Examination - Start with examination for surface integrity, deposits, lens surface and edges
(chipped). Review the lens fitting. The lens parameters are known to change with the passage of time,
especially the soft lenses. These changes can lead to steeper fittings later. Evaluate both static and
dynamic fitting with fluorescein dye in case of RGP lenses.
Re-examine without Lenses Next
 Slit-lamp Examination - Check the corneal integrity, stain the cornea with the fluorescein dye and
look for any aberrations and staining. Make an optical section of the slit and look for any edema.
Specular reflection technique should be utilized to note any endothelial changes. Evert the upper lid
now to examine the upper tarsal conjunctiva. Look for CLPC.
 Keratometry - Keratometry should be repeated and recorded on follow up visit to see if there is any
effect of lens wear on the cornea.
 Refraction - Do subjective refraction after about 30 minutes of lens removal. Compare the findings
with the base line record. Marked changes like myopic shift or increasing astigmatism will warn
against the corneal changes happening with the lenses.
 Dry Eye Tests - Dry eye or dryness is the most common complaint, more so with soft lenses. Dry eye
tests like Schirmer and BUT should be done after removing the lenses.
CONTACT LENS COMPLICATIONS
Although contact lenses are generally regarded as safe, yet they are associated with a small risk or
complications. Detection of these anatomic changes and the initiation of appropriate management can
often prevent more serious threats of vision loss.

Corneal Ulcer Infected — (Serious Complication)

Infected corneal ulcers are the most serious complication associated with contact lens wear. An ulcer is
defined, as the full thickness epithelial loss with stromal necrosis and inflammation, may be central or
paracentral.
Etiology
It is thought that hypoxia leads to reduction in ability of the eye to resist invading organism. The most
important organisms leading to serious infections are Pseudomonas aeruginosa and Acanthamoeba.
The infection can be passed on from patient’s contaminated hands, lens case, solution or may be an
improperly disinfected lens.
That is again related to hypoxia, which is most likely with extended wear soft lenses.
Symptoms
 Foreign body sensation to extreme pain
 Redness
 Mucoid discharge (bacterial), watery (viral), purulent to watery (fungal)
 Photophobia
 Reduced visual acuity if ulcer is in pupillary area.
Signs
 Intense redness, generally diffused but can be localized
 Usually unilateral
 Opaque white area in the cornea
 Infiltrates
 Lid edema
 May be associated with anterior chamber flare.
Management
 Remove lenses immediately
 Refer for medical treatment—includes corneal scraping for smear and culture prior to treatment,
start broad spectrum antibiotic therapy.
 No lens wear for 2- 3 months
 Refit with new lens and reinsure compliance.
Prevention
In the prevention of ulcer the patient and the practitioner play a very important role. One can reduce such
sight-threatening complications if:
  Patient/practitioner is aware of the warning signs
 He does not sleep with the lenses (unless recommended)
 Stress on proper hygiene and compliance
 Home made saline and tap water have a higher risk of infection
 Regular follow-ups even if there is no complaint.
CLPU—Contact Lens Peripheral Ulcer
This is a round full thickness epithelial loss with inflamed base, typically in corneal periphery, which
results in scar.
They are generally small ulcers less than 1 mm in diameter. They are also not associated with any sign of
anterior chamber flare and stain with fluorescein dye.
Corneal Neovascularization
It is the growth of the limbal blood vessels into the cornea. The vessel extension beyond translucent
limbal zone is recorded in millimeters. Small amounts 1 to 2 mm are common, more than 2 mm is a
warning sign. If this progresses into the visual axis it can lead to vision loss. It may be superficial deep,
superficial or all around 360 degrees into the cornea.
Etiology
The most common reason is hypoxia. Others include solution sensitivity, or mechanical effects like poor
fit or damaged lens.
Symptoms
• Asymptomatic
• Vision effected if vessel growth is over pupil.
Signs
• Vessel growth seen around limbus
• It may be looped if inactive or branching if active.
Management
• Discontinue wear till vessels are emptied of blood
• Refit with higher oxygen permeable lens
• Advice daily wear mode only
• Discontinue wear permanently if severe neovascularization.
Prevention
• Regular follow-ups and examination
• Refit with better oxygen transmissibility lenses if NVE observed.

Corneal Edema — Striae and Folds

Edema is the swelling of the cornea due to increased accumulation of the fluid in the stroma. Edema leads
to separation of collagen fibrils and if increases lead to corneal haze.
Chronic levels of corneal edema, even if low, result in adverse effects on functioning of the cornea.
Symptoms
• Patient is symptomatic only if the corneal edema is greater than 20%
• Higher levels cause glare, haloes around light and decreased acuity.
Signs
Observe in optical section of the cornea
• Striae—fine grayish white vertical lines mostly in the posterior stroma (One striae signifies 5%
edema)
• Folds—fine grey lines, buckling of the posterior cornea (One fold signifies 8% edema)
• Each additional striae or fold indicates 1% more edema.
• Loss of corneal transparency if edema is more than 20%.
Management
• Edema resolves in around 3 hours after removal of lenses
• Chronic edema may take one week to resolve
• Refit with higher oxygen transmissibility lens
• Decrease wearing time.
Precautions
• Commonly found in extended wear
• Refit when warning signs are first seen
• High plus powers should be carefully followed, as central thickness is more.

Inflammatory Ocular Responses

Infiltrates
Infiltrates means the infiltration of the cornea with aggregates of the inflammatory cells such as
neutrophils, macrophages, and lymphocytes. This happens as an inflammatory response to the stimuli.
They are white opacities observed epithelial, subepithelial or stromal depending upon the layer of the
cornea.
Etiology
They occur in conjunction with acute red eye, corneal ulcer or infection, localized trauma, solution
sensitivity and prolonged hypoxia. The incidence of infiltrates is more in soft lenses used for extended
wear.
Symptoms
• May be asymptomatic, depends upon severity
• Photophobia
• Foreign body sensation
• Watering
• Redness or pain
• Depending upon the etiology.
Signs
 • White opacities most frequently seen 2 -3 mm from limbus
• May be focal or diffuse.
Management
• Discontinue lens wear
• Treat the underlying etiology by determining the cause.
Prevention
• Prevent recurrence based on the etiology
• Refit with RGP if reoccurs with soft lenses.

CLARE—Contact Lens Acute Red Eye

It is a serious inflammatory response reaction reported frequently with extended wear lenses.
Etiology
Red eye is an inflammatory response that can be from hypoxia to contamination to an ill-fitting lens.
Symptoms
• This is typically seen in extended wear patients who wake up with painful red eye in the morning
• It may be associated with watering and photophobia
• Vision is affected if it is severe.
Signs
• Associated with infiltrates
• Redness
• Usually unilateral.
Management
• Discontinue lens wear
• Refer for medical intervention – antimicrobial therapy if due to infection
• Resume lens wear after 2 weeks.
Prevention
• Avoid extended wear
• Check fitting particularly avoid steep fitting
• Proper hygiene
• Frequent replacement
• Warn patient of the warning signs.
Contact Lens-induced Papillary Conjunctivitis—CLPC (Giant Papillary Conjunctivitis)
CLPC is the inflammatory response of the upper tarsal conjunctiva. The smooth conjunctiva becomes
rough, bumpy and uneven. The condition progresses from mild to severe stage if the predisposing factor
is not removed. GPC is one of the major reasons for lens dropouts. Its incidence reduces remarkably if the
lenses are replaced frequently. CLPC is less likely to occur with RGP lenses.
Etiology
This is an inflammatory response that is induced by the deposits or any mechanical interaction between
lid and lens.
Symptoms
• Depends upon the grade and severity
• Stage 1 is preclinical and patient is asymptomatic
• Itchiness
• Mucous strands
• Lens intolerance/reduced wearing time
• Excess lens movement.
Signs
• Enlarged papillae—bumpy upper lid on eversion
• Lid redness
• Mucus strands
• Lens moves more.
Management
• Discontinue lens wear till GPC subside—may be one or two months
• Shift patient to FRP
• No extended wear
• Find the cause and treat.
Prevention
• Early detection by regular follow-ups
• Frequent replacement program
• Enzyme treatment to reduce deposits.

Sensitivity to Solutions
The preservatives in the solutions can cause immediate allergic reactions or delayed hypersensitivity
reactions. The patient develops an inflammatory reaction.
Symptoms
• Reduced tolerance to lenses
• Gritty sensation
• Dryness
• Itching.
Signs
• Superficial corneal damage
• Redness—mild to moderate
• Infiltrates (may be)
• Papillae.
Management
• Cease use of preserved solutions
 • Try other preservative group
• Shift patient to unpreserved unit doze solutions with thermal disinfection or peroxide system of
disinfection
• FRP—frequent replacement program.

Epithelial or Subepithelial Corneal Staining

Corneal staining can be identified with fluorescein dye. Any damage to the cornea can be seen as green
stain seen with slit lamp and cobalt blue light. With all aberrations the lens wear should be ceased.
Superficial epithelial damage will heal within 24 hours. Deeper ones diffused into the stroma may take 2
to 7 days.
Staining can be of various types and typically diagnostic of several complications. It should be routine to
instill fluorescein in the eye and examine for any corneal staining.
Corneal staining may be seen in—corneal aberrations, superficial punctuate keratitis, 3 and 9 o’clock
staining, arcuate defects or dry eye.

Corneal Aberrations
They occur because of some mechanical trauma to the eye. This may be due to fingernail, a foreign body
under the lens or mechanical pressure due to a tight or flat fit. These aberrations are more commonly
found in RGP lenses. With an aberration on the eye the patient is at risk to microbes that can penetrate the
cornea easily. It is also seen that aberrations infected with pseudomonas lead to serious corneal ulcers.
Symptoms
• The patient is uncomfortable
• Pain
• Watering
• Intolerance to lens wear.
Management
• Discontinue wear till aberration heals
• Treat the cause
• Prevent chances of infection
• Refit if improper lens.

Toxic Staining
Solution preservatives can cause toxic reactions. A typical diffuse superficial punctuate staining all over
the cornea can be seen with the slit-lamp.
Symptoms
• Discomfort
• Burning and stinging sensation soon on insertion of lens.
Signs
 • Conjunctival redness
• SPK—superficial punctuate keratitis.
Management
• Change solutions
• Shift to unpreserved system of disinfection

Superficial Epithelial Arcuate Lesion—SEAL

Epithelial defect in arcuate pattern often at the periphery or mid-periphery, usually superior, may be seen
in a tight fitting soft lens or also due to pressure of lid on the lens.
Symptoms
• May be asymptomatic.
Signs
• Superior arcuate shaped lesion staining with fluorescein dye.
Management
• Change to different lens type material and design
• Use a well-blended peripheral curve design
• Consider RGP.

3 and 9 o’ Clock Staining

This condition of corneal staining is typically seen in rigid lenses. It is caused by desiccation of the cornea
which occurs as a result of an interruption of tear flow or tear layer at the nasal and temporal cornea.
The disruption of the tear layer can be because of a poor edge fitting.
− A flat lens on astigmatic cornea
− A wide edge of an daily wear lens
− Low riding lens with edges touching the nasal and temporal cornea
− Poor wettability of the lens
− Narrow edge if the RGP is for extended wear mode
− This staining can also be because of patients poor tear quality. Patients who avoid blink to reduce
lid interaction ultimately develop this kind of staining
− Persistent staining will lead to stromal thinning and dellen formation.
Symptoms
• Intolerance to lens wear
• Dryness.
Signs
• Typical staining at nasal and temporal cornea—the 3 and 9 o’ clock position
• Redness of conjunctiva at these positions
• Infiltrates in advanced cases.
Management
• Identify the cause
• Modify the edge design
• Improve blinking
• Check tear quality
• Use in eye lubricants
• Refit with larger diameter.
THERAPEUTIC CONTACT LENS
Therapeutic lenses are also called bandage lenses that are used to treat a range of external ocular surface
disorders primarily affecting cornea.
The Therapeutic Lenses Principle Aim is to Bandage the Eye Serving as a Therapy which
• Provides relief from pain.
• Serves mechanical protection by separating the epithelial surface from the external agents such as
lid surfaces, thus protecting the epithelium.
• Seal corneal perforations by acting as a splint for the underlying weaker tissues and supports the
area while healing takes place.
• Corrects the surface irregularities in irregular corneas and improves visual acuity.
Unlike normal corneas the eye to be fitted with therapeutic lens is a compromised eye and is at higher risk
of hypoxia and infections. The balance between benefits and potential risk must be carefully considered.
Conditions of Eye which are Suitable for Therapeutic Lenses
1. Eyelid abnormalities—entropion, trichiasis, ectropion, lagophthalmos
2. Ocular surface disorders—chemical injuries, dry eye, Stevens- Johnson syndrome
3. Corneal surface disorder—recurrent erosion syndrome, keratitis, traumatic epithelium
abnormalities, filamentary keratitis, bullous keratopathy.
Selection of the Lens
The lens type is selected on the following criterias:
• Oxygen Transmissibility - High water content, thin mid water content lenses, silicone hydrogels or
high Dk RGP lenses give the best transmissibility. Lenses which have to be worn for extended periods
should be selected from either of these materials.
Select high water contact lens in eye conditions where the lens has to act as a splint. RGP lenses as
discussed earlier are for irregular compromised corneas to achieve better vision.
• Diameter - Soft bandage lenses are usually larger in diameter usually 14.0 to 15.0 mm.
• Power - Bandage lenses are usually plano in power.
• Disposable Lenses or FRP Lenses - Disposable lenses or FRP lenses are selected as bandage lenses.
Therapeutic lenses should be preferably discarded after every use. They are nowadays rarely cleaned
and reinserted. Deposits formation is very likely and heavy in such eye conditions.
Fitting Guidelines
 Keratometry it is usually not possible to determine the corneal curvature in such eye conditions. The
mires are heavily distorted. Corneal topography or Keratoscopy can give some useful information in
selecting curvatures.
 In case of traumatic corneas, the good eye K reading can form a base line to start with, on the
assumption that the corneal curvature may have been same before trauma in the eye to be fitted with
contact lens.
 Anterior segment assessment is important. Staining if possible should be done with rose Bengal dye
and recorded and graded. Also the eye should not be in acute infective state during fitting. Tear film
stability should also be measured.
 Select the type of lens according to the eye condition
 For soft lenses - allow the lens to settle on the eye may be for 15 to 20 minutes
− Optimal fit—reasonably well centered
− Complete coverage of the cornea.
− Movement slightly restricted at the same time does not allow the debris to accumulate behind.
About 0.3 to 0.5 mm with each blink.
− Observe the eye condition after 4 hours, then 24 hours of wear. Ensure there is no
complication developing because of the lens and the wound has started healing.
− In most cases the bandage lens is worn for short periods of extended wear, regular follow-ups
are important.
− It is the practitioner who inserts and removes these lenses whenever needed. However, the
patient should also be explained the emergency removal technique and contact lens care and
maintenance. He should have a container with the soaking solution at hand with him.

 RGP
− Measure the good eyes keratometry in case of uniocular disorders as base line.
− The fitting is done on hit and trial basis.
− There should not be excessive bearing or clearing areas. The tears should exchange properly and
debris should also not collect behind the lens
− Achieve a stable centered lens.

COLORED CONTACT LENSES

Colored soft lenses are also used in practice. Besides cosmetic reasons, they also form a part of
therapeutic lenses.
Reasons to fit a soft colored lenses contact lens are:
 Cosmetic reasons
 Traumatic and post surgical scars
 Pthisis bulbi
 Aniridia
 Albinism
 Diplopia
 Amblyopia therapy.
The tints used in practice are of three types:
1. Visibility tint
2. Cosmetic tints
3. Prosthetic tints.
Visibility (Handling) Tint
Soft lenses are usually white and transparent. Certain tints, like the light blue or green transparent tints are
added to improve the visibility of the lens to the patient during lens handling procedures. These do not
affect the eye color when worn.
Cosmetic Tint
They are used to enhance or change the eye color. They are available in plain or in powers. They are of
two types
 Transparent
 Opaque
The tinted zone of the soft lens covers the iris color and changes or enhances it.
Transparent Tints - These lenses transmit 70% of the light. They are available in various shades. The tint
is in the form of a concentric ring, which has a clear centre pupil.
Opaque Tint - They absorb or reflect all incoming light, therefore used to completely change or mask the
underlying eye color. They have an iris pattern, with a clear central pupil. The clear pupil is typically 5
mm in diameter.
Prosthetic Contact Lenses
They are fitted to enhance the appearance of a damaged or injured eye or as an occluder in amblyopia
therapy.
They can be clear center or dark center. The pupillary zone selected can be clear or opaque depending
upon the cosmetic and the visual requirement.
Even with best materials and designs, one cannot match the normal looking eye yet can enhance their
quality of life.
Tinting Methods
 Dye dispersion: The dye is added to the monomer, before polymerization. The final color is uniform
and throughout the lens. The thickness of the lens can vary the shade.
 Vat dye process: The lens is firstly soaked in a hypotonic solution. The matrix thus expands. The
water-soluble dye is absorbed in the matrix. This is then converted into a water insoluble dye. The
lens is removed from the hypotonic solution. The matrix shrinks and the dye is trapped.
 Covalent bonding: The lens surface is reacted with the dye and then bonded chemically to the matrix.
 Print transfer process: The tint or the pattern is printed onto the surface of the lens.

Fitting Guidelines for Prosthetic Lens

Fitting prosthetic lens is not different from fitting standard lens. The difficulty lies in determining a
proper fit for an abnormal iris, pupil and cornea.
The easiest method is to take healthy eye as the model and take measurements of pupil size, iris diameter
and keratometry. Evaluate the condition and the health of the eye. Finally match the colors—select from
the available colors closest to the eye.
Several times there are limited parameters available but it is usually sufficient for most of the eyes. One
may have to order a custom design lens parameters and eye shade for an individual with matching pupil
and iris size.
CONTACT LENS FITTING AFTER REFRACTIVE SURGERY
The fitting of contact lenses after refractive surgery is a challenge for the majority of eye care
professionals. Not only are there problems because of limited designs for oblate corneas but in addition
many patients opt for refractive surgery in the first place due to contact lens intolerance. In such cases,
patients require encouragement and psychological support during the process of fitting. Incisional
techniques such as radial and astigmatic keratotomy cause corneal alterations that are different from those
techniques in which tissue is removed, such as photorefractive keratectomy (PRK) and laser in situ
keratomeleusis (LASIK). For this reason, the fitting of contact lenses in each of these classes of surgery is
detailed separately.
Indications for fitting contact lenses after radial keratotomy
 Undercorrection
 Overcorrection
 Irregular astigmatism
 Anisometropia
 Progressive hyperopic shift
 Glare
 Fluctuating vision
Contact lens options after radial keratotomy
 Spherical rigid gas permeable contact lenses with high oxygen permeability (Dk).
The first choice of treatment should be a rigid gas permeable (RGP) contact lens. This lens,
supported on the mid-peripheral cornea, stabilizes vision by creating a smooth and consistent
optical surface. An ideal lens of this type is one made of fluorosilicone acrylate because of its high
oxygen permeability. It permits better oxygen transmission to the cornea with less risk of
complications compared to polymethylmethacrylate (PMMA), RGP lenses with a lower Dk, and
hydrophilic lenses.
 Hydrophilic contact lenses
Soft hydrophilic contact lenses do not offer the benefit of stable and clear visual acuity because of
the flexible nature of the material. In addition, because of lower oxygen permeability, they may
increase the risk of corneal neovascularization to the incision scars.
 Special designs (both hydrophilic and rigid gas permeable lenses)
 Piggyback systems
A piggyback system—the combination of a soft lens under an RGP lens—is an option for patients
with RGP intolerance. However, even with the advent of silicone extended wear disposable soft
lenses, this system has the disadvantage of being more expensive, less convenient, and less
healthy for the cornea than a RGP lens alone.
 Hybrid contact lenses (Softperm)
A hybrid lens offers greater convenience than piggyback systems but is more expensive and offers
less oxygen transmissibility to the cornea. Both the rigid center and the soft skirt have a lowDk,
which may lead to hypoxic conditions. This is complicated by the fact that these lenses tend to
tighten on the eye, further increasing the risk of neovascularization and corneal edema. Both
piggyback and hybrid options should therefore be avoided unless no other successful alternatives
are available.
Primary indications for fitting contact lenses after LASIK
 Overcorrection
 Undercorrection
 Perforation, dehiscence, decentration, or loss of the flap
 Irregular astigmatism or surface irregularities
 Stromal haze or scarring
 Corneal ectasia

Types of contact lenses are used in fitting post-LASIK patients

 Hydrophilic contact lenses (spherical or special designs)
 RGP lenses (spherical, aspheric, and reverse geometry designs)
 Piggyback systems
 Hybrid lenses

MANAGEMENT OF PRESBYOPIA WITH CONTACT LENS

Presbyopia
Presbyopia is part of the normal aging process, where the eye loses its ability to easily focus on near
objects. Emmetropes, who have never worn glasses, will also require plus power to focus on near objects
one has to just “Add” plus power to the patient’s distance prescription to provide a lens that can focus on
the near objects. We all know that presbyopia can be corrected by several options in spectacle form it can
be by:
− Single vision reading glasses, bifocals, trifocals or multifocals With contact lenses on the eye there are
two options to correct near vision with spectacles over CL.
Option 1 is:
− Fit CL for distance; do not overcorrect
− Determine near addition over CL on trial frame
− Prescribe reading glasses over CL.
Option 2 is:
− Ideal for patients who do near/intermediate work all day
− Give near add on CL
− Give minus power for distance in the form of spectacles for driving and other distance task.

Patient Selection
Screening the patients is the key to success. Those who are likely to respond positively to presbyopic
correction with contact lenses are the ones who are:
 Highly motivated
 Those who have adequate tear film and no lid disease or abnormality
 Have low hyperopia
 Whose jobs do not require fine visual acuity
 Affordability.
Contact Lens Presbyopia Correction
Three main types of contact lens for the presbyopic correction are:
− Monovision correction
− Alternating/translating vision lenses
− Simultaneous vision lenses.

Monovision
Monovision is the technique in which one eye is corrected for distance vision and the other eye for near
vision. This is not occlusion. It works on the principle that the visual system can suppress the central
focus image thus enable the object of interest to be seen clearly. There is some disruption of binocularity
in this fitting methodology. Still Monovision remains the easiest and an effective means of correcting
Presbyopia. The success rate is as high as 70%. This is the only technique by which we can correct the
existing rigid lens wearers for near (as the options of bifocal RGP lenses are not yet available in our
market). We can also convert emmetropes into contact lens wearers by simply fitting one eye for near.
Fitting Procedure for Monovision
1. Determine the distance and near prescription
2. Determine the dominant and the non-dominant eye.
To do this, do the following test:
 Ask the patient to look at any distance object, may be a spot light or a bright colored dot target
fixed at about 6 m distance or may be the 6/60 alphabet of the Snellen’s chart.
 Let the patient hold a card with a circle of about 2 inches diameter at arms length
 Ask the patient to binocularly see through the circle, the distance spot light or any other target
selected.
 Now alternately close his either eye. Ask through which eye, is he actually seeing the spot
light.
 The patient will be able to see through one eye only. This is the dominant eye.
3. Fit the dominant eye with the distance power prescription and the non-dominant eye with the near
power prescription. Suppose the patient’s prescription is:
RE : –4.0 Dsph and LE : –4.0 Dsph
Near add +1.50 Dsph both eyes.
Now fit the dominant eye with –4.0 Dsph (the distance power) and the non-dominant eye with –2.50
Dsph (the near power).
4. Use disposable lenses for this, and give an in-office trial. Record binocular visual acuity for distance
and near. Most of them will be satisfied to see the magic of now being able to see for distance and
near. Do not attempt uniocular visual acuity now. Obviously the eye with near power will read less for
distance and the eye with distance power will read less for near.
5. Explain the fitting technique now. Reassure that this will not harm his eyes.
6. Some patients may need some adaptation time and may be dissatisfied with the reduction of
stereopsis.
7. Follow up, and fit the final lens.
Tips for Monovision fitting
− Adaptation time allowed should be at least 2 weeks
− Advise patients to continue normal activities if possible
− No night driving
− Do not compare eyes
− Set patient’s expectations
− Educate visual improvement over time.

BIFOCAL/MULTIFOCAL CONTACT LENSES

Translating Vision Type
The patient must look and alternate through two separate portions to see either near or distant objects.
This is just like our executive type bifocal spectacle lenses. The patient when looks down gaze the lower
lid lifts the near segment up, towards the pupil or the visual axis thus the patient can see clear for near.
This type of bifocal design is popular in rigid lens wearers. It needs a little more skill in fitting so that the
position of the distance and the near segment is proper. In this design the near and far cannot be seen
clearly at the same time. The fitting is assessed best with the Burton lamp than the slit lamp, so that it
shows the position of the segments in more natural postures.
Advantages

 Sharp near/far vision

 When it works well, it is very successful
 Works better in RGP and less successful/common in SCL.

Disadvantages

 Takes longer in adaptation

 Comfort is less due to thick design
 Dependence on eye-lens relationship.

Simultaneous Vision
In this type the distance and near images are focused on retina (fovea) simultaneously.
The brain will select or concentrate on one or other will be ignored. It is just like looking through the net
across the window at a distance object. One must have noticed this that despite the net in the visual area
the brain ignores it and you can see clear the distance target.
This technique may lead to “Ghosting” (doubling) of image, which may sometimes create a problem. Still
it is the most popular option now in bifocal lenses.
Advantages

 Sharp near and far vision.

Disadvantages

 Compromised intermediate vision.

 Ghosting (doubling) is sometimes a problem.
Simultaneous vision lenses are further of three types:

 Concentric (segmented)
 Diffractive
 Aspheric.

Concentric Design
Concentric segment lenses show a sharp demarcation between distance and near powers.
They are of two types:
− Center near
− Center distance
Central Near Segment

 Reading induced miosis, so it is good for patients who have more of near work to do
 In bright light the lens is biased for near.

Central Distance Segment

 Pupil position is important in this design

 Halos may occur, if the pupil size exceeds the distance segment
 Interference from the segment images may be disturbing.

Pupil Size Dependency

There is dependency of these designs upon the pupil size. A center near will cause blurred vision for
distance in bright light if the pupil constricts too low, and the distance center design can cause ghost
images in night specially during driving.
Image clarity is relatively independent of pupil size like in multi-concentric design of Acuvue bifocal
lens.

Diffractive Bifocal
Diffractive bifocal is made up of concentric rings, something like a Fresnel prism. Higher the addition
more the number of rings.

 It has multiple circumferential Fresnel type prisms

 The distance and near images are focussed at the same time
 Pupil size is not important
 May not be good for excessive night driving
 Contrast sensitivity is reduced in this design.

It is most suitable for people who work in different light conditions.

Aspheric Designs
This is a progressive addition type of lens formed with alteration in anterior and posterior curvature of the
lens. The power uniformly increases/ decreases in periphery due to the asphericity
  No ghosting as in concentric design
 Clarity of vision at all distances
 Simplified fitting
 Used mostly for office workers
 Disadvantage—pupil dependency.

It is of two types:
Aspheric back surface lens design

 Fit well over aspheric cornea

 Has Aspheric posterior curve
 Increasing PLUS power peripherally
 Provide central distance correction

Used in patients who need better distance vision in bright light.

Aspheric front surface lens design

 Aspheric anterior curve

 Back surface is spherical
 Increasing PLUS power centrally
 Provide central near correction.

Modified Monovision
This is a technique where one eye is fitted with distance correction and the other eye is a bifocal lens.
This improves the binocularity and stereoacuity which may be reduced in Monovision. This technique is
also tried in patients who are sensitive to distance vision.
Unsuccessful contact lens fitting is likely in presbyopes who are:

 High myopes
 Patients with busy schedules
 Dry eyes
 Flat corneas
 Laxity of lower lid
 High astigmatism
 Or any other external ocular disease or abnormality.

PAEDIATRIC MANAGEMENT WITH CONTACT LENS

Children are different from adults because they have different ocular surface, configuration and different
physiology which is needed for the contact lens fitting.
Secondly children do not allow all the parameters and the trials to be done on the eye as easily as adults.
We all know that the reasons of fitting contact lens are not cosmetic. The basic principle is to allow more
normal development of Visual Acuity and prevent or minimize amblyopia.
The reasons to prescribe contact lenses in children < 5 years are:

 High myopia
 Moderate to high hyperopia,
 Moderate to high anisometropia
 Amblyopia
 Nystagmus
 Corneal masking
 Bandage contact lens.

Children are fitted with contact lenses in moderate to high degrees of refractive error for simple reason
that contact lenses have following advantages over spectacles:

 Reduce peripheral distortions

 Reduce aniseikonia
 Reduce prismatic imbalance
 Inappropriate correction in spectacles may interfere with emmetropization
 Better control in Eso deviations with contact lenses due to base out prism effect.

Contact Lens in Aphakic Child

This forms the largest part of pediatric Contact Lens Practice. We all know that favorable prognosis
depends on surgical, optical correction followed by amblyopia therapy. CL reduces image size to 8%
compared to 33% with glasses. This forms the major reason to fit lenses in this group. The aphakic
spectacles are usually around +20 diopters in power, which make the glasses very heavy and unsightly.
Indication in Amblyopia
Occlusion contact lens is very useful for children who resist occlusion over spectacles with patches or
occluder. Special contact lens with center opaque pupil and dark iris contact lenses are very easily
acceptable to the parents also. One has to overrule the advantage over the risk of infections with the
lenses. Second problem is that it has been seen that children can manipulate lens off cornea by rubbing
the eyes. The major decision has to be from parents, who have to learn lens handling.
Cosmetic CL in Children
Cosmetic reasons to fit lenses in children are
• To mask opaque corneas
• Use in severe photophobia
• Aniridia, albinism, etc.
Remember the advantages have to overrule risks.
Contact Lens in Nystagmus
Contact lens moves with visual axis so there are less distortions and prismatic effects, which will reduce
the amplitude of nystagmus and hence better visual development.
As Bandage Lens
Contact lenses in children have same therapeutic reasons as in adults that is mostly for healing of
epithelial aberrations as in trauma. It is very rare to find pediatric dystrophies and corneal syndromes.
Ocular Configuration Changes in Childhood
Compared to adults the child has following ocular change:
1. Have less lipid deposits
2. Have increased aqueous—hence good oxygen supply and maintains lubrication
3. Smaller palpebral aperture which inhibits insertion and removal.
4. Crying may lead to still tight closure of lids.
Paediatric Cornea
Before fitting lenses one must know the corneal dimensions in a child as this forms the basis of contact
lens curvatures. These changes may affect the fit.
Corneal Diameter Changes in Childhood
The cornea in a child increases rapidly in first year of life and slowly thereafter.

 It is about 10 mm at birth
 About 11.5 mm at 4 years of age
 In microcornea and microphthalmia – diameter may range from 6 to 7 mm
 In megalocornea and high myopia diameter may range from 14 to 15 mm.

Corneal Curvature Changes in Childhood

 At birth about 47 to 49 D
 Rapid flattening in the first 6 months
 It flattens to 43.5D by 4 years of age.
 During first year the peripheral cornea is steeper which gradually flattens with age and growth.

Lens Designs and Materials for Children

Children can be fitted with either of these material lenses.

 RGP
 Soft
 Silicone elastomer.

The choice should be to give a lens that provides sufficient oxygen suitable as extended wear, comfort
and vision. The lens should also be easy to handle for the parents.
Soft Contact Lens
This lens material has an advantage that it is comfortable. The comfort of the lens keeps the child quiet
and willing.
Soft lens material in children has the following disadvantages:

 Difficult handling and insertion because they are large in size for their small palpebral apertures.
 Prone to deposits—like all soft lenses
 Infection risk in extended wear
  Limited parameters are available in soft lenses for pediatric age group. Lathe cut lenses or custom
designs have to be ordered for children.
Rigid Gas Permeable Lens
Rigid lens materials as far as possible should be the lens of choice, due to its basic advantage of sufficient
oxygen transmissibility.

 Easier for parents to handle

 Wide range of parameter available
 Excellent oxygen permeability
 Well tolerated due to moist eye.

Rigid lens materials in children have following difficulties:

 They are difficult to fit as one needs to align the lens curvatures to the atypical corneas.
 There is initial discomfort, which may discourage the parents and scare the child.
 Since these lenses move freely on the eye there is a possibility of lens dislodgment with rubbing.
 There may be corneal insult due to rubbing and rough insertion of these lenses.

Silicone Elastomers
Only available for pediatric aphakes in this group is the B&L – (Silsoft lens). It has enormous oxygen
permeability but tends to coat lipids easily. This material is the only safe extended wear lens for children.
Now continuous wear silicone hydrogels are also available, they work as very safe and best lenses, if the
suitable parameters are available for the child’s eye.

Fitting Technique
Fitting Under GA
GA is recommended by some practitioners as it facilitates easy measurements, but involves risks of GA.
Fit assessment is also found to be inaccurate under GA because:

 Lid position and forces are different in prone position

 Lacrimation is absent
 Decreased IOP which may change corneal shape

Use it only when it is impossible.

Six Steps to Fit Infants and Very Young Children
1. Examine the eye: To rule out that the eye is ready for CL
2. Determine parameters for CL: Based on the ocular configurations some possible selections can be
made even if the ocular dimensions are not measurable.
a. Select a lens diameter
 Soft lens - 12 to 13 mm
 RGP lens - 9 to 9.5 mm
 Silicone elastomer - 11.3 mm
b. Select a base curve
 Soft / silicone—one step steeper than the usual adult lens
  RGP—0.10 to 0.20 mm steeper than usual.
c. Central thickness: Standard to thick, thin lenses should be avoided.
d. Lens power: The power of the lens should be ordered about 2- 3 diopters over plus than the
spectacle refraction.
The starting powers in aphakic according to age are usually found to be:
6 months = +30
1 year = +27
2 years = +23
3 years = +21
3. Evaluation: Evaluate the lens fit by checking the position and movement of lens. Wrap the infant
properly in the sheet and hold him comfortable over the bed or mother’s lap. Crying or squeezing will
not allow you to assess the fit. Be calm and try to evaluate with the baby distracted or attracted by
parents or relatives.
a) In case of Soft and Silicone lens
 Central position
 Movement less than adults
 Lens should not decenter more with blink and push up test.
b) Fitting evaluation in RGP lens
 Check position with torch and white light
 Evaluate fluorescein pattern, with direct ophthalmoscope and blue filter
 Prefer lid attachment fit
4. Determine the final lens power: After finalizing base curve and diameter do over refraction. Overplus
infants by 2.5 to 3 D to give them the near working distance.
5. Finalize: See that the lens is stable on eye. Visibility or handling tint should be used. Ultimately again
check that you prescribe a lens with sufficient oxygen to allow safe napping.

Instruction and Follow-up

Communication with parents is critical. Explain the risks and warning signs and the expenses. Reinforce
that their efforts will make the child see better all life. This will encourage them to bear up with the
shortcomings.
 Insertion/removal - both parents should be instructed:
− Restraint technique - Hold the child arms above head close to the skull therefore immobilizing the
head and arm movements. The second person holds the legs together.
− Straddling technique - the baby is swathed in thick blanket from neck downwards enveloping the
rest of the body.
Follow-up
Children need to be followed up frequently, (monthly, 3 monthly) on every visit check:
 Compliance
 Over refraction
 Visual acuity—Teller’s or HTOV charts
 Evaluate lens fit changes—this happens often as the cornea and the ocular dimensions are
changing rapidly, especially in early years of life. Remember the child’s eye needs sufficient
oxygen. The child is active so one has to fit a lens with more stable position, a lens that is more
durable and easy to handle.