INTRODUCTION TO

VISION PRACTICAL
HMP 100 / V28 100/ U29 100

Dr Teresa Kinyari Mwendwa

University of Nairobi
College of Health Sciences School of Medicine
Department of Medical Physiology

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Anatomy
 Anatomy

 Extraocular movements

 Medial
 Lateral
 Upward
 Downward
 Visual Acuity
 General physical examination should include :
 Visual acuity
 Pupillary reaction
 Extraocular movement
 Direct ophthalmoscope
 Dilated exam (in case of visual loss or retinal
pathology)
 Distance or Near
 Distance visual acuity at age 3
 early detection of amblyopia
 Definition

 The resolving power of the eye used to assess and

quantify the eye’s ability to resolve varying letter sizes
 Visual acuity is dependent on:
 The refractive error of the eye
 The health and the integrity of the eye
 The test targets used
 The test conditions
 Measurement

 The measurement of VA is done to monitor change in

vision with disease progression of disease and/or
treatment plan
 It is a way to measure “blur” vision
 Visual acuity must be measured on every patient at
every visit!
 Standard Test Distances

 Distance visual acuity (DVA)

 20ft or 6M is equivalent to optical infinity
 Near visual acuity (NVA)
 40cm
 Weymouth Classification of
Visual Acuity Measurements

 Minimum distinguishable (or minimum visible)

 The ability to see something as being
distinguishable from the background
 Minimum separable
 The ability to determine a group of points or lines
as separate and distinct
 Minimum cognizable or legible
 The ability to form sense (e.g., Landolt C) or
minimum legible (e.g., letters or numbers)
 History

 Early astronomers found two stars resolvable as separate if

the distance between the stars subtend an angle of at least
1 minute of arc
 Snellen Test

 In 1862 Snellen and Giraud-Toulon introduced a

system for measuring VA
 A form of minimum legible visual acuity task
 Snellen acuity is based on a minimum angle of
resolution of 1 minute of arc
 Visual acuity target designs: optotypes
 The Snellen optotype has overall dimensions that are 5
times the detail
Typical Snellen Optotype
 Snellen Notation
 Snellen fraction
 Test distance divided by the distance at which optotype
would subtend 5 minutes of arc at the retina
 The denominator of the Snellen fraction is termed
the foot-letter size
 The letter’s overall size, both angularly and linearly
 The average emmetrope has a VA of 20/20 or
better
 This is based on a test distance of 20ft
 The classic Snellen fraction is the reciprocal of the
minimum angle of resolution (MAR)
 Snellen Acuity and Minimum
Angle of Resolution
Snellen Acuity Snellen Acuity Minimum Angle
of Resolution
Fraction Decimal Minutes of Arc
20/20 1.0 1
20/25 0.80 1.25
20/30 0.67 1.5
20/40 0.50 2
20/50 0.40 2.5
20/100 0.20 5
20/200 0.10 10
Snellen Chart
 Snellen Test

 Snellen equivalent
 If the test distance is not 20ft, the measured
Snellen fraction may be used to predict what the
patient’s VA would be for a 20ft distance
 Example
 Patient can resolve a 30ft letter at a test distance of
15ft. The Snellen acuity is 15/30.
 15/30 =20/x
 x = 40
 The Snellen equivalent is 20/40
 Calculating a Visual Acuity Test
Object’s Foot-Letter Designation
 Example of a letter that is 2cm tall
 Types of Distance
Visual Acuity Charts

 Wall charts
 Testing VA in literate adults
 Printed on cardboard and mounted on a wall
 Well-suited for vision screenings and doctors’ offices
 Variations: Tumbling E chart, Landolt C chart, Bailey-
Lovie chart
Tumbling E Chart
Landolt C Chart
Bailey-Lovie Chart
 Types of Charts

 Hand-held visual acuity cards

 Primarily for children in vision screenings
 Simplest form is the letter E in different sizes printed
onto hand-held cards
 Free space testing
 Types of Charts

 Chart projectors
 Projects test objects onto a screen
 Standard chart projector can be calibrated for varying
testing distances between 10ft and 20ft
 Optically “fold” the testing distance using mirrors to
create appropriate testing distance (20ft is the standard)
 Calibration of Chart
Projectors

 Measure the testing distance

 Calculate how large an optotype would have to be on
the screen to represent 20/200 for that testing
distance
 Adjust the lenses in the chart projector until the letter
size from the previous step is achieved
Chart Projector Set-Up
 Calibration of Chart
Projector

 A 20 foot-letter is 8.87mm. May use direct

proportions to calculate the letter size that would be
needed to represent 20/20 for any possible testing
distance.
 Example
 8.87mm/20ft = x/17ft
 x = 7.54mm
 Recording

 Record the VA line for which more than 2 letters (or

less than half the number) are read incorrectly
 Recording

 Examples
 Two out of five letters on the 20/20 line are read
incorrectly
 20/20 -2
 All letters on the 20/20 line are read correctly, and one
letter on the next line down is read correctly
 20/20 +1
 One of the letters on the 20/20 line is read incorrectly, and
two letters on the 20/15 line are read correctly
 20/20 -1/+2
 Recording

 Points to consider
 Ask the patient to read a line over again or show the
letters to the patient one line at a time
 Isolate lines on the chart to avoid distracting influences
 May consider showing the patient a line of the same VA
on a different slide, if the projector has more than one
slide
 Expected Findings

 A visual acuity of 20/20 or better is considered normal

 The difference between the two eyes should be no
greater than one line
 Pinhole Visual Acuity

 Purpose
 To determine if a decrease in vision is correctable
by lenses
 Pinhole visual acuities are taken when the
patient’s entering VA is worse than 20/30 at
distance and near through the habitual
correction
 Expected Findings

 If the cause of the patient’s decreased visual acuity is

due to an uncorrected refractive error, the VA is
expected to improve through the pinhole
 If the cause of decreased visual acuity is not optically
based, no improvement, and possibly a decrease, will
occur through the pinhole
Pinhole Effect
 Near Visual Acuity

 Testing the VA at close range (usually 40cm)

 Near visual acuities are taken through the habitual
correction
 The purpose is to detect people with near vision
difficulties (e.g., uncorrected high hyperopia,
accommodative dysfunction)
 In patients over 40 years old, the reduced near visual
acuity is one of the symptoms of presbyopia
 Near Vision Charts

 Types of notation
 Reduced Snellen Acuity card
 Test distance at 16in (or 40cm)
 Jaeger Acuity Card
 20 letter sizes classified J1 to J20
 Test distance at 14in
 Point system
 Each point is 0.35mm
 M notation
 Based on meter unit
Bailey-Lovie Reading Card
Lea Symbols
 Rosenbaum pocket
Snellen eye chart chart
 Distance Visual
Acuity Testing

 Place patient at 6 metres from Snellen chart

 OD then OS
 VA is line in which > ½ letters are read
 Pinhole if < 6/12
 6/6

Distance between the patient and the eye chart in metres

_____________________________________________

Distance at which the letter can be read by a person with

normal acuity in metres
 Near Visual
Acuity Testing

 Indicated when
 Patient complains about near vision
 Distance testing difficult/impossible

 Distance specified on each card (35cm)

 Pupillary Examination

 Direct penlight into eye while patient looking at

distance

 Direct
 Constriction of ipsilateral eye
 Consensual
 Constriction of contralateral eye
 Ocular Motility

Rt superior rectus Lt superior rectus

Lt inferior oblique Rt inferior oblique

Rt lateral rectus Lt lateral rectus

Lt medial rectus Rt medial rectus

Rt inferior rectus Lt inferior rectus

Lt superior oblique Rt superior oblique
 Direct
Ophthalmoscopy

 Tropicamide or phenylephrine for dilation

 unless shallow anterior chamber
 unless under neurological evaluation
 Use own OD to examine OD
 Same for OS
 Intraocular Pressure
Measurement

 Range: 10 - 22
 Anterior chamber
depth assessment

 Likely shallow if
 ≥ 2/3 of nasal iris in shadow
Astigmatism
Astigmatism
 Principles of Visual Field
Testing and Perimetry

 Why are visual fields performed ?

 (a) It is the only clinical test that measures peripheral

visual function.

 (b) Visual fields improve detection of disease (many

ocular and neurologic deficits affect peripheral vision
before the fovea or macula is involved.
 PURPOSE

 This procedure measures in diopters a patient’s ability

to change the focus of the eye’s crystalline lens in
response to a near stimulus.
 EQUIPMENT

 Near point visual acuity card.

 Tape measure in centimeters.
 Occluder.
 SET-UP

 The patient is tested wearing his habitual distance

correction. This test may also be performed behind
the phoropter as a part of the post-refraction
phorometry sequence.
 Either the patient or the examiner may hold the near
point card.
 The near point card should be well-illuminated.
 STEP-BY-STEP
PROCEDURE

 Instruct the patient to occlude his left eye to test the right
eye.
 Direct the patient’s attention to a row of letters one or two
lines larger than his near VA.
 Instruction the patient to keep the letters clear.
 Slowly move the chart closer to the patient and ask the
patient to report when the letters become and remain
blurry.
 STEP-BY-STEP
PROCEDURE

 Measure the distance from the chart to the patient’s

spectacle plane in centimeters. The linear measurement is
referred to as the near point of accommodation.
 Convert the linear distance into diopters by dividing the
near point of accommodation in centimeters into 100. The
resulting dioptral value represents the patient’s amplitude
of accommodation.
 Occlude the right eye and test the left eye using steps 1 to
6.
 RECORDING

 Record the method of testing used.

 Record the amplitude of accommodation in diopters
(round off to the nearest half diopter).
 Separately record the results for the right and left
eyes.
 EXAMPLES
 Amp (push-up) OD 7.0D OS 7.0D
 Amp (push-up) OD 6.0D OS 6.0D
 EXPECTED FINDINGS

 The expected amplitude of accommodation decreases with age. The two most
commonly used systems for obtaining the expected amplitude of
accommodation are
 A. Hofstetters’ formulas
 Minimum expected amplitude = 15 – 0.25 (age)
 Average expected amplitude = 18.5 – 0.30 (age)
 Maximum expected amplitude = 25 – 0.40 (age)

 Donder’s table for age-referenced amplitude of accommodation

 The amplitude of accommodation of the two eyes should be within one diopter
of each eye.
 Donder’s table

Age Amplitude Age Amplitude

10 14.00 45 03.50
15 12.00 50 02.50
20 10.00 55 01.75
25 08.50 60 01.00
30 07.00 65 00.50
35 05.50 70 00.25
40 04.50 75 00.00
 Fundoscopy

 https://youtu.be/YP1nbM3x-uU
Principles of Visual Field Testing
and Perimetry
Fundoscopy
Fundoscopy
 Why are visual fields
performed ?

(c) Visual fields provide useful differential diagnostic

information – the pattern and location of visual loss is
specific to damage at particular locations along the
visual pathways, unlike visual acuity loss, which is not
very specific.

(d) Many people are unaware of peripheral vision loss,

particularly if it is gradual, and even if it affects their
ability to perform daily tasks such as navigation, etc.
 A cookbook for visual field
evaluation

(a) Place the left eye visual field on the left and the right
eye visual field on the right.

(b) For each eye, is the visual field normal or abnormal ?

(If normal in both eyes, you’re done)

(c) If abnormal, is it one eye or both eyes ?

(d) If in one eye, it’s retina or optic nerve.

 A cookbook for visual field
evaluation

(e) Where is the defect ? (sup, inf, nasal, temporal)

(1) Nasal or binasal – glaucoma, optic nerve or retina

(2) Bi temporal – chiasm

(3) Nasal in one eye, temporal in the other –

postchiasm
 A cookbook for visual field
evaluation

(f) What is the shape (features) of the defect ? Respect

the vertical, respect the horizontal, point to the blind
spot, point to fixation, etc.

(g) How do the two eyes compare ? (homonymous,

congruous) (h) Where is the most likely location of the
deficit ?
 Key features to
remember

(a) Respect the horizontal - Glaucoma, optic nerve,

retina

(b) Respect the vertical - Chiasm, post-chiasm

(c) Point to the blind spot - Optic nerve, glaucoma

(d) Point to fixation - Chiasm, post-chiasm

 Key features to
remember

(e) Bitemporal – Chiasm

(f) Homonymous - Post-chiasm - The greater the

congruity between eyes, the farther back in the optic
radiations.

(g) Central - Retina, optic nerve

 Types of deficits

(a) Optical factors (cataract, corneal abnormalities) - Usually

diffuse or widespread losses

(b) Retinal Disease - Ring Scotomas (retinitis pigmentosa),

arcuate defects (branch artery occlusion), central and
centrocecal (between the blind spot and fixation – candle
flame shaped) irregular (scalloped) edges to deficits.

(c) Glaucoma - Nasal steps, paracentral defects, arcuate

scotomas, temporal wedges, fan-shaped defect that points
to the blind spot.
 Types of deficits

 (e) Chiasmal lesions (pituitary adenoma, pituitary

apoplexy) – Bitemporal defects. Defects point to
fixation and vertical meridian is respected.
 (f) Lateral geniculter lesions – Are very rare. Deficits
appear as a tongue shape along the horizontal
meridian or the tonue is the only remaining visual
field.
 Types of deficits

(g) Post-chiasmal defects (temporal lobe, parietal lobe,

occipital lobe deficits) The vertical meridian is respected

(1) Temporal Lobe – Defects are “pie in the sky” deficits and
are incongruous between eyes and point to fixation.

(2) Parietal lobe - Defects are “pie on the floor” are more
congruous between eyes and point to fixation.
(3) Occipital lobe - Cookie cutter punched out lesions that
are highly congruous between eyes and point to fixation.
 Summary of steps
in eye exam
 Visual Acuity
 Pupillary examination
 Visual fields by confrontation
 Extraocular movements
 Inspection of
 lid and surrounding tissue
 conjunctiva and sclera
 cornea and iris
 Anterior chamber depth
 Lens clarity
 Tonometry
 Fundus examination
 Disc
 Macula
 vessels
 Visual acuity is described as:
a) A phenomenon called spatial discrimination
b) A measure of the acuteness of vision of a
subject for near vision
c) The ability to see near objects clearly
d) Emmetropia at visual acuity of V6/18
e) Myopia at visual acuity of V6/6
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2. During normal visual acuity assessment:
a) The subject sits 6 meters away from the
chart
b) Each eye is assessed separately
c) The left hand is used to cover the right eye
d) Snellen’s chart is placed 3 meters in front of
the subject
e) Hyperopia is diagnosed at visual acuity of
V6/5
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  Refractive index of the eye include the
following EXCEPT the :
a) Aqueous humor
b) Iris
c) Vitreous humor
d) Optical lens
e) Cornea
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 Myopia correction

Figure 1
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The correction for visual acuity defects shown in Figure 1 above:
a) Required convex lenses which converge the light on the
retina
b) Is done using a visual acuity lens frame with normal lenses
c) Results in divergent of light rays to form the image behind
the retina
d) Show concave lenses which bring the image to the front of
the retina
e) Results in spatial discrimination of the object with image at
the retina
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 Figure 2

The Snellen’s chart shown in

Figure 2 above is used in :
a) Near point assessment
b) Visual acuity assessment
c) Colour vision testing
d) Astigmatism testing
e) Visual perimetry mapping

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  Colour vision assessment is done using the following
charts:
a) Snellen’s
b) Ishihara
c) Visual field
d) Landolt ring
e) ‘E’ test

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Makena got the pair of lenses shown in the figure below. The
following statement is FALSE:
a) C1 converges the image formed behind the eye back to
retina
b) The correction by the C2 is to diverge light impinging on the
lower half of the cornea
c) This is her prescription for correction of emmetropia in
both eyes
d) At the age of 65 years to correct the visual acuity defect of
presbyopia in both eyes
e) Which brings together two centers of visual focus into one
clear image
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