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Low Vision Assessment and Rehabilitation

Article  in  Delhi Journal Of Ophthalmology · August 2017

DOI: 10.7869/djo.282

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Low Vision Assessment and Rehabilitation
Rebika Dhiman, Itika Garg, Sneha Aggarwal, Rohit Saxena, Radhika Tandon
Low Vision Services, Dr R P Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
Low vision and blindness are a growing health problem that adversely affects the quality of life of an
individual. Low vision rehabilitation (LVR) is the process of restoring functional ability and improving
quality of life and independence of a patient with low vision. Currently India is a home to around one-
Abstract third to one-fourth of the world’s blind population. Lack of awareness about the low vision services are
a major drawback in the rehabilitation of a low vision patient in our country. Thus, in this article we
discuss about the methods of evaluation of a patient with low-vision and prescription of low vision aids.

Delhi J Ophthalmol 2017;28;7-12; Doi; http://dx.doi.org/10.7869/djo.282

Keywords: low vision aid, low vision rehabilitation, low vision, blindness

Introduction
Table 1: Diseases leading to Low Vision:Presentation as per
World Health Organisation (WHO) defines Low Vision Anatomical Site
(Visual impairment Categories 1 & 2) as “A person who has
Anatomical Site Diseases presenting with
impairment of visual functioning even after treatment and/
Low Vision
or standard refractive correction, and has a visual acuity
of less than 6/18 to light perception, or a visual field less Microcornea, Adherent
Leucoma, Corneal Opacities,
than 10 degrees from the point of fixation, but who uses, Cornea Bullous Keratopathy,
or is potentially able to use, vision for the planning and/ Microspherophakia,
or execution of a task for which vision is essential” and Dystrophies
Blindness (Visual impairment Categories 3, 4 & 5) as “Visual Congenital cataract, Ecotpia
acuity of less than 3/60 or a corresponding visual field loss Lens Lentis or Dislocated IOL,
of less than 10 degrees in the better eye with best possible Uncorrected Aphakia
correction.”1,2 The term visual impairment includes both Coloboma of Iris or Choroid,
blindness as well as low vision. Uveitis, Chorioiditis,
Uvea
The classification by NPCB (National Program for Control Aniridia, Choroidal
of Blindness) defined low vision as “Visual acuity of less Degeneration
than 6/18 but equal to or better than 6/60 in the better eye Persistent Primary
with available correction or a visual field loss of less than Vitreous Hyperplastic Vitreous
10° from the point of fixation”, and, blindness as “Visual (PHPV)
acuity less than 6/60 in the better eye or a corresponding Heredo-Macular
visual field loss of less than 10°.”3 Recentlly the definition Degeneration, Stargardt’s
Dystrophy, Rod-Cone
of blindness has been revised by NPCB so as to bring about
Dystrophy, Retinitis
uniformity with the WHO criteria.4 Pigmentosa, Age-Related
Based on the current estimates, worldwide there are 161 Retina Macular Degeneration,
million people with visual impairment; out of which 37 Oculo-Cutaneous Albinism,
million are blind and rest 124 million are people with low Retinopathy of Prematurity,
vision.5 Ninety percent of the people with visual impairment Retinal Scars. Fundal
Coloboma, Diabetic
are living in the developing countries. Currently, India has Retinopathy
around 12 million blind people which makes India home
Optic Neuropathy
to one-third of the world’s blind population.6 With the
Optic Nerve (Traumatic, Ischaemic,
increasing life expectancy and thus increasing age related Congenital), Glaucoma
problems, the magnitude of visual impairment is expected
Ocular Motility Squint, Nystagmus
to rise in coming years.
Low vision is one of the priority areas of VISION 2020. Microphthalmos,
Hence, visual rehabilitation of a patient with low vision, Pthisis, Absolute Eye,
where further intervention is unlikely of any benefit, is Retinoblastoma, Atrophic
Globe
Bulbi, Pathological Myopia
of paramount importance and need of the hour. Table 1
or High Refractive errors,
enumerates various causes of low vision. Amblyopia
Low vision rehabilitation (LVR) is the process of restoring
Cortical blindness, Delayed
functional ability and improving quality of life and Visual Pathway
Visual Maturation
independence of a patient with low vision. It requires a
thorough clinical and functional assessment of the disease, rehabilitation is tailored to correspond to the type of the
of patients’ requirements and daily needs. Thereafter, the visual disability and the individual’s expectations.

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Goals of Comprehensive Low Vision Examination and 3. Refraction

Visual Rehabilitation All visually impaired patients should undergo
a. Identify and evaluate the cause of low vision refraction to ensure optimal correction for achieving
b. Assess ocular health best corrected visual acuity. Most low vision devices
c. Emphasize the need of the patient/ beneficiary are used in conjunction with refractive correction.
d. Clinical Assessment The presence of uncorrected presbyopia or significant
e. Maintain and improve visual function uncorrected refractive error could affect success with
f. Optometric rehabilitation & intervention low vision devices.
g. Counsel and educate Tips for Refraction in patients with low vision:
h. Appropriate visual rehabilitation
 Auto-refractors have limited use, due to media
Patient evaluation: problems or eccentric viewing (off axis fixation).
1. Patient history is an essential pre-requisite for low
vision examination  Previous glasses can be a good starting point
It should include
- Nature and type of the problem  Keratometry can be useful to determine the amount
- Onset and duration of the presenting problem and axis of cylinder.
- Condition-stable or progressive Patient may have difficulty in fixation.
- Visual difficulties
- Chief complaints  Retinoscopy is most useful tool for refraction
- Visual and ocular history, including ocular history for low vision, especially if the patient is poor
of family members; responder.
- General physical and mental health Amount of magnification can be calculated based on
- Social history; the present visual acuity and the required visual acuity
- Use of low vision devices or history of vocational, (a) If VA is measured in a LogMAR notation:
educational or any other training. Magnification = (1. 25)n
- General examination- Details regarding name, Where n = number of steps
age, address, family members, current profession, If the present acuity = 0.5 and the required acuity =
current academic status, financial status and 0.1
information about the disorder (cause, time of Then Magnification = (1.25)4 = 2.44x
onset, family history) are equally important.
2. Visual acuity Assessment (b) Magnification required = Required VA
Distance Visual Acuity Measurement: It not only gives Present VA
a baseline to monitor the pathology, but also helps to
predict the magnification level of the optical devices. In Snellen notation to improve from 6/60 to 6/6
It is also essential to establish legal blindness, driving
privileges, job eligibility etc. Magnification required = 6 x 60
=10x
Snellen, Bailey-Lovie, LogMAR or Feinbloom charts 6x6
can be used for distance acuity measurement. LogMAR 4. Ocular Motility and Binocular Vision
chart is considered to be ideal as there is a uniform Assessment
progression of letter sizes with a standardized Gross assessment of ocular alignment, binocularity and
separation of letters. stereopsis is needed.
Specific activities customized as per the need of 5. Visual Field Assessment (Figure 1)
profession of the patient should be checked. The size and location of the scotoma can affect reading
- Blackboard/TV for school going children ability, despite appropriate magnification and visual
- Recognising faces or reading bus number or metro acuity improvement. Visual field assessment is
stations for adults important for orientation, mobility training, to guide
- Photophobia from sunlight, glare from car light in patient for preferred retinal fixation or environmental
night must be recorded. modifications Assessment can be done using:
- Need for different lights in different environments - Confrontation method for gross field defect is
must be checked for proper low vision aid trial. evaluated.
- Mobility must be noted; if the patient is independent - Amsler or threshold Amsler grid assessment - The
or requires support in familiar or unfamiliar presence of significant distortion may hamper the
locations. quality of vision.
Near Visual Acuity Measurement is of paramount - Goldman Perimetry – It is very useful to quantitatively
importance as most low vision patients struggle with locate the size and extent of scotoma, to evaluate
reading. It is important to specify the near point acuity tunnel vision or peripheral visual field loss.
with the reading distance.

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Prescription of Low Vision Aids (LVA)
Before prescribing LVA in a patient, we need to define
the patient’s goals and develop his skills in using these
devices. The basic principle of all optical low vision device
is magnification. Magnification can be achieved in four
different ways (Table 2).
(1a) (1b) (1c) I. Near Optical Low Vision Devices:
1. Spectacle magnifiers (Figure 2) are high powered convex
lenses that are prescribed as reading glasses. They can
be spherical, aspheric with and without base-in prisms.
Reading material is held at a distance that is equivalent
to the focal distance of the lens. Major disadvantages
are fixed close reading distance and a constricted field
(1d) (1e) (1f) of view.
2. Hand held magnifiers (Self-illuminated and Non-
Figure 1: Visual field assessment in a patient with low vision. (A)
illuminated) (Figure 3) are plus lenses that are held in
Confrontation method for visual field; (B) Amsler grid; (C) Amsler grid
depicting metamorphsia; (D) Goldman perimeter; (E) Goldman visual field front of the spectacle plane. It is convenient for short
– central scotoma; (F) Goldman visual field – Tunnel vision. tasks like reading signs, labels, prices, books, identifying
money etc. It has a limited field of view and requires
6. Ocular Health Assessment good hand eye coordination.
- External examination (adnexa, lids, conjunctiva, cornea, 3. Stand magnifiers (Figure 4) are mounted on a rigid
iris, lens, and pupillary responses) stand. The patient needs to place a stand magnifier
- Biomicroscopy (lids, lashes, conjunctiva, tear film, on the reading material and move across the page
cornea, anterior chamber, iris, and lens) to read. A reading stand is recommended with this
- Tonometry kind of magnifier. They are preferred in patients with
- Central and peripheral fundus examination under constricted visual fields or central visual field loss. Too
dilated pupils, unless contraindicated close reading posture makes it difficult to be used for
7. Supplemental Testing long hours.
- Glare testing - Patients with albinism, cataract, Table 2: Types and principles to achieve magnification
posterior capsular opacification, aniridia, corneal No Type of Principle Formulae
opacities, corneal edema, glaucoma, lasered Magnification
proliferative diabetic retinopathy, etc may suffer from 1 Relative Size Enlargement RSM = New Size
glare. Testing glare acuity signifies the need to add Magnification of the size of Reference Size
filters or contrast enhancers to improve the distance (RSM) the object
vision. Glare disability can be tested objectively No optical
system
by using glare acuity tester and auto refractors, or
subjectively by patients’ complaints, comparing the 2 Relative Moving the RDM = Reference Distance (r)
Distance object closer New Distance(d)
visual acuity with or without illumination in vision Magnification to subtend a
chart. (RDM) larger angle
- Contrast sensitivity is related to the visual functioning on retina
more closely than visual acuity. Contrast assessment Optical system
can be done with Pelli-Robson contrast sensitivity required
chart at one meter, Lea contrast flip chart, Hiding Heidi 3 Lens Vertex Angular M=
Magnification Magnification angle subtended by image at eye
contrast test chart. A patient with low contrast acuity (M) angle subtended at unaided eye
will have to be prescribed a low vision aid with higher
4 By Telescopic By electronic
than expected magnification, higher illumination and/ systems systems
or absorptive filters or typoscopes.
- Color vision Testing - It can be done by Ishihara’s
pseudoisochromatic color plates, or by asking the
patient to discriminate, match or sort out various color
threads or buttons.
- Electrophysiological tests (Electroretinogram (ERG),
Electro-oculogram (EOG), Visually Evoked potential
(VEP)) – It is very helpful in patients of cortical
blindness, LCA, mentally retarded patients, infants (2a) (2b)

or kids where the visual acuity cannot be estimated

subjectively and has a poor visual prognosis. Figure 2: Spectacle magnifiers (A) Different types of spectacle magnifiers;
(B) Close reading with reading magnifier.

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and OrCam. These electronic devices are capable of

recognizing text, objects, currency etc.9
Off late, devices like smart phones, tablets and electronic
readers are being increasingly used as low visual aids.
Incorporated with the features of zoom, high-contrast
screens, invert colors and bespoke apps, these internet-
ready devices have proved to be valuable tool for low
vision patients.10-12
(3a) (3b)

II. Low Vision Devices for Distance:

1. Telescopes (Uniocular or Binocular) (Figure 6) magnify
the apparent size of distant objects, making them
appear closer to the patient than they actually are. The
optics is based on two principles (Table 3) - Galilean or
Keplerian. Telescopes are expensive and have restricted
field of view. Bioptic Telescope is a system where the
(3c) (3d)
telescope is attached to the top of a pair of eyeglasses.
It allows the wearers to switch their sight between their
Figure 3: Hand held magnifiers (A) Hand Held and Foldable magnifiers; “regular vision” and the magnified vision of the device
(B) Position while reading with a hand held magnifier; (C) Self-Illuminated by just a slight tilt of the head, similar to how one uses
and Non-Illuminated hand Held Magnifiers; (D) Magnification with
magnifier.
bifocal spectacles.13,14

(4a) (4b) (4c)

(4d) (4e) (4f)

Figure 5: Hand held video magnifier

Figure 4: Stand magnifiers (A) Cut away stand magnifier; (B) Adjustable
stand magnifier; (C) Reading stand; (D) Close reading with stand
magnifier; (E) Dome magnifier; (F) Neck magnifier.
4. Digital Devices- This linear magnification device is
controlled by a zoom lens attached to the camera.
This helps in obtaining a higher magnification with a
normal reading distance by varying the addition and
the reading distance. Near work such as writing and Figure 6: Telescopes
(A) Uniocular hand held
typing can be done more easily with this device. Closed telescope;
(6a)
circuit television (CCTV) may be the only choice for (B) Spectacle mounted
patients whose vision is too impaired to benefit from telescope.
routine optical aids. These devices could be a hand held
(Figure 5) or a desktop magnifier. A study has reported
a faster reading speed in patients using CCTV than
other optical devices.7
With the recent technological advances in the field of
LVR, several portable electronic low vision devices
have become available that are considered to be cost-
effective than most other low vision aids.8 Some of
these devices are Optelec Compact+, Optelec Compact (6b)
4HD, Schweizere Mag43, Eschenbach Mobilux Digital

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Table 3: Principles of telescopic system

Galilean Telescope Keplerian Telescope

1. Eyepiece – negative lens, Objective – positive lens 1. Both Eyepiece & Objective – positive lens
2. Image – virtual and erect 2. Image – real and inverted
3. Loss of light reduces the brightness of image to 3. Loss of light is more in the system-greater loss of
some extent brightness
4. Field quality is relatively poor 4. Field quality is relatively good

2. SEE TV Spectacles are also known as TV glasses low vision services still remain low due lack of awareness
and comes with 2.1 to 3x magnification. It is useful amongst the patients as well as the ophthalmologists.15-18
in students while watching blackboard, desktop or Hence, a low vision clinician should be aware of the range
television. They are commonly used at a distance of 3 of specialists, vocational services and community based
metres. services needed by people with low vision.

Non-optical devices for visual rehabilitation References

Non-optical devices improve the visual function by altering
illumination and light transmission, reducing reflection and 1. WHO. International Statistical classification of diseases,
injuries and causes of death, tenth revision, 1993.ICD –
glare, enhancing contrast, and linear magnification. Classification of Diseases, Functioning, and Disability. Atlanta
Non-visual or non-optical devices are used for profound (GA): National Center for Health Statistics; Available from:
visual impairment to assist in supplementing and improving http://www.cdc.gov/nchs/icd.htm; International Updated
visual function. Sept 1 2009; cited Feb 17 2010.
- Medical devices with signal or voice 2. WHO/Priority eye disease. Available at: www.who.int/
blindness/causes/priority/en/index4.html.
- Reading machine
3. National Program for the Control of Blindness. Available at:
- Travel device www.npcb.nic.in
- Talking book, clock, calculator and watches. 4. The definition of blindness under NPCB. Available at: npcb.
- Typewriter –Audiologic equipment. nic.in/index1.asp?linkid=55.
- Filters or tinted lenses 5. WHO/ Visual impairment and blindness. Available at: http://
www.who.int/mediacentre/factsheets/fs282/en/print.html.
These include notex, typoscope, signature guide, lamp,
6. Dandona L, Dandona R, John RK. Estimation of blindness in
filters/tints, contrast enhancers to aid activities of daily India from 2000 through 2020: implications for the blindness
living and enlarged fonts. control policy. Natl Med J India 2001; 14:327-34.
There are certain things to be kept in mind before 7. Virgili G, Acosta R, Grover LL, Bentley SA, Giacomelli G.
prescribing low vision aids. Patient’s expectations Reading aids for adults with low vision. The Cochrane Database
should be discussed and the limitations of the prescribed Sys Rev 2013;10:CD003303.
8. Bray N, Brand A, Taylor J, Hoare J, Dickinson C, Edwards
device should be explained. The power of magnification RT. Portable Electronic Vision Enhancement Systems in
prescribed should be as low as possible in order to give a Comparison With Optical Magnifiers for Near Vision
wider field of view. After prescription of LVA, a thorough Activities: An Economic Evaluation Alongside a Randomized
training should be conducted to enable the patients to use Crossover Trial. Acta Ophthalmol. 2016 Sept 29. [Epub ahead
the devices smoothly. The family should be counseled for of print].
9. Moisseiev E, Mannis MJ. Evaluation of a Portable Artificial
environmental modification and supportive services to
Vision Device Among Patients With Low Vision. JAMA
utilize the residual vision maximally. Ophthalmol 2016; 134:748-752.
Low vision rehabilitation is a new emerging sub-specialty 10. Mednick Z, Jaidka A, Nesdole R, Bona M. Assessing the iPad
that aims to improve the functionality and independence of as a tool for low-vision rehabilitation. Can J Ophthalmol 2017;
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11. Walker R, Bryan L, Harvey H, Riazi A, Anderson SJ. The value
approach. Despite the advances in the field, uptake of

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of tablets as reading aids for individuals with central visual 17. Khan SA, Shamanna B, Nuthethi R. Perceived barriers to the
field loss: an evaluation of eccentric reading with static and provision of low vision services among ophthalmologists in
scrolling text. Ophthalmic Physiol Opt 2016; 36:459-64. India. Indian J Ophthalmol 2005; 53:69–75.
12. Robinson JL, Braimah Avery V, Chun R, Pusateri G, Jay WM. 18. Pollard TL, Simpson JA, Lamoureux EL, Keeffe JE. Barriers
Usage of Accessibility Options for the iPhone and iPad in a to accessing low vision services. Ophthalmic Physiol Opt 2003;
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71.
13. Owsley C, McGwin G, Elgin J, Wood JM. Visually impaired Cite This Article as: Dhiman R, Garg I, Aggarwal S, Saxena R, Tandon
drivers who use bioptic telescopes: self assessed driving R. Low Vision Assessment and Rehabilitation.
skills and agreement with on-road driving evaluation. Invest
Ophthalmol Vis Sci 2014; 55:330–6. Acknowledgements: Nil
14. Bowers AR, Sheldon SS, DeCarlo DK, Peli E. Bioptic Telescope
Use and Driving Patterns of Drivers with Age-Related Macular
Degeneration. Trans Vis Sci Technol 2016; 5:5. Conflict of interest: None declared
15. Kovai V, Krishnaiah S, Shamanna BR, Thomas R, Rao GN.
Barriers to accessing eye care services among visually Source of Funding: Nil
impaired populations in rural Andhra Pradesh, South India.
Indian J Ophthalmol 2007; 55:365–71.
16. Khan SA, Shamanna B, Nuthethi R. Perceived barriers to the Address for correspondence
provision of low vision services among ophthalmologists in
India. Indian J Ophthalmol 2005; 53:69–75.
Rebika Dhiman MD
Senior Research Associate
Dr. R. P. Centre for Ophthalmic Sciences
All India Institute of Medical Sciences
Ansari Nagar, New Delhi, India
Email id: drrebika@gmail.com

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