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 Table of Contents  
COMMISSIONED ARTICLE
Year : 2022  |  Volume : 10  |  Issue : 3  |  Page : 137-143

An updated approach to low-vision assessment


Department of Ophthalmology, AIIMS, Gorakhpur, Uttar Pradesh, India

Date of Submission03-Feb-2022
Date of Decision28-Oct-2022
Date of Acceptance03-Nov-2022
Date of Web Publication1-Dec-2022

Correspondence Address:
Alka Tripathi
Department of Ophthalmology, AIIMS, Kunraghat, Gorakhpur - 273 008, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jcor.jcor_22_22

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  Abstract 


The 2017 Global Burden of Disease study ranked vision impairment, including blindness, as the third cause among all impairments for years lived with disability visual impairment has enormous social and economic consequences in terms of productivity losses and dependency. Seeing the rapidly increasing burden of low vision (LV) globally, and more specifically, in the developing world, there is a need to have the provision of good quality LV care as a key element of the comprehensive eye service. The assessment of a visually challenged client by an ophthalmologist or optometrist is substantially different from a standard or routine examination in an ophthalmology unit. Eye professionals should be prepared to spend twice or thrice the amount of time spent on routine eye examinations. An accurate assessment of visual, functional, and psychological needs leads to clarity in prescribing appropriate LV devices. LV rehabilitation is the only nonsurgical treatment modality for vision impairment and this review article throws light on this overlooked aspect of eye services.

Keywords: Low-vision devices, low-vision assessment, quality of life, telescopes, vision rehabilitation


How to cite this article:
Tripathi A, Agarwal R. An updated approach to low-vision assessment. J Clin Ophthalmol Res 2022;10:137-43

How to cite this URL:
Tripathi A, Agarwal R. An updated approach to low-vision assessment. J Clin Ophthalmol Res [serial online] 2022 [cited 2023 Jan 31];10:137-43. Available from: https://www.jcor.in/text.asp?2022/10/3/137/362502



The 2017 Global Burden of Disease[1] study ranked vision impairment, including blindness, the third cause among all impairments for years lived with disability. Vision impairment causes restrictions in independence, mobility, and education, and increases the risk of falls, fractures, comorbidities, poor mental health, and cognitive deficits resulting in social isolation.

The term “Visual impairment” includes both LV and blindness. The definition of LV and blindness may vary between countries. The most accepted definition is as given by the World Health Organization (WHO) according to which low vision (LV) is visual acuity (VA) 3/60 to <6/18 in the better eye after the best possible correction in the better eye and visual field <20° from the point of fixation.[2] Near vision, impairment is presenting near VA worse than N6 or N8 at 40 cm when best corrected VA was ≥6/12 (20/40).[1],[3]

International Statistical Classification of Diseases and Related Health Problems, 10th Revision (ICD-10) Version for 2010[4] categorizes visual impairment into five categories based on presenting VA. Previous definitions were based on best-corrected VA of the better eye, the current definition is based on presenting VA (with glasses if any and without glasses if not) to emphasize the burden of uncorrected refractive errors. ICD-10 states LV as moderate (category 1) and severe visual impairment (category 2) which means VA worse than 6/18 and equal to or better than 3/60 and those with a visual field ≤20°. LV (category 1 and 2) candidates are targets for vision rehabilitation. Blindness (Category 3, 4, 5) is defined as VA of <3/60, or a corresponding visual field loss to <10°, in the better eye with the best possible correction[4] [Table 1]. These candidates have the partial vision and should be tried for blind rehabilitation which includes sight substitutes such as braille instruction and/or long-white-cane training.
Table 1: Classification of visual impairments according to the International Classification of Disease-10 2016 revision

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Faye[5] categorized causes of LV are shown in [Table 2]. LV aids prescribed usually depend on whether a visual impairment is central, peripheral, or hazy.
Table 2: Causes of low vision according to Eleanor E. Faye

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  Epidemiology Top


According to the WHO and the International Agency for the Prevention of Blindness vision report, in 2019,[6] 2.2 billion people have a vision impairment or blindness. Among these, 1 billion have a vision impairment that could have been prevented or has yet to be addressed.[7] The leading causes of vision impairment are uncorrected refractive errors and cataracts.[1],[8] [Figure 1] shows the estimated global number of people with vision impairment that could have been prevented or has yet to be addressed.
Figure 1: Estimated global population with vision impairment that could have been prevented or has yet to be addressed according to WHO-IAPB vision 2019 (reporthttps://www.iapb.org/wp-content/uploads/world-vision-report-accessible1.pdf). WHO-IAPB: World Health Organization- International Agency for the Prevention of Blindness

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Vision impairment and blindness caused by eye conditions such as glaucoma, age-related macular degeneration, corneal opacity, and diabetic retinopathy cannot be treated and rehabilitation is required. Vision rehabilitation aims to make maximal use of residual vision and provide practical adaptation to address the psychological, social, emotional, and economic consequences caused by visual impairment.[9] A LV candidate should be examined in light of certain goals which are mentioned below.

Goals of LV assessment (LVA) and rehabilitation:[10]

  • Identify patients who might benefit LV care and rehabilitation[11]
  • Evaluate the functional needs
  • Evaluate the impact of ocular and systemic diseases on functional vision
  • Evaluate the need for LV devices (LVD)
  • Evaluate the need for educational/vocational guidance
  • Counsel the patient, family, and other care providers (including teachers/employers) about the visual disability
  • Appropriate referrals to professionals (such as speech therapists and psychologist).


The assessment of a visually challenged client by an ophthalmologist or optometrist is substantially different from a standard or routine examination in an ophthalmology unit. Eye professionals should be prepared to spend twice or thrice the amount of time spent on routine eye examinations. The basic steps involved in LVA are as follows:

  1. Clinical evaluation
  2. Functional evaluation
  3. Vision rehabilitation.



  Clinical Evaluation Top


Observation, review of medical record, and history taking

It is important to review past medical and surgical reports for any treatable cause of LV that might have been overlooked.[12] Observation of visual behavior can provide important preliminary information about the visual status which includes how the patient negotiates his/her visual environment (ability to perform near, intermediate, and distant tasks). Observe interactions with the family members, and employment issues (social history). Observation of postural abnormalities, mobility, and appearance-head turn or tilts found with peripheral field defect. Presence of nystagmus, eye poking/oculo-digital syndrome, tentative gait, maintenance of proximity to walls or handrails, reliance on tactile information by holding onto an individual (indicative of peripheral field defect), eye contact while answering questions.

Cognitive functions should be assessed followed by the identification of priority tasks for rehabilitation such as reading requirements and desires, ability to perform activities such as writing, sewing, cooking, and viewing the computer, ability to travel independently, and any difficulty in functioning in bright sunlight, indoors lighting and at night or visual requirements for their job.[13] In the case of a child, requirements vary according to a special school or mainstream regular school The effect of vision LV on the person's daily activities, any other disability (hearing impairment or orthopedic handicaps), psychological considerations (e.g., denial, depression, co-dependency, or suicidal tendencies), or any visual hallucinations (repeating pattern of lines, dots or other geometric shapes, picture, landscapes) should be well reviewed.

Charles Bonnet syndrome (CBS)[14] is a condition that some people get when they lose some or all their vision. It causes them to have visual hallucinations (seeing things that are not there). There is as such no cure for CBS. The patient should be encouraged to rest and relax, can change their environment, and share their hallucinations to get relief from the anxiety.[15]

The effect of LV on the quality of life (QoL) can be assessed by the National Eye Institute (NEI) Visual Function Questionnaire (VFQ) which is a self-reported vision-targeted health status questionnaire for persons who have chronic eye diseases.[16] The 25-item version (VFQ-25) generates the following vision-targeted subscales: global vision rating (1) difficulty with near vision activities, (3) difficulty with distance vision activities (3) limitations in social functioning due to vision, (2) role limitations due to vision, (2) dependency on others due to vision,(3) mental health symptoms due to vision, (4) driving difficulties, (3) limitations with peripheral (1) and color vision, (1) and ocular pain. (2) It is the reduced version of the 51-item NEI-VFQ.[17] Higher scores on these scales correspond to a better QoL. Realistic patient goals found during the examination are important in the exploration of rehabilitation options.

By the end of completion of the case history, the clinician has an impression of the patient's objectives and goals, whether or not they are realistic, the patient's reaction to the vision loss, and discern how much time to spend with the patient.

Visual acuity assessment

Distance visual acuity

The log minimum angle of resolution (MAR) test charts fulfill most of the requirements of a LV chart, i.e., has high contrast, geometric progression of a size difference between lines, and proportional spacing of optotypes, a consistent number of letters in each row, allows testing at nonstandard testing distances of 3 m or closer [Figure 2]. Some of the commercially available log MAR charts are Early Treatment Diabetic Retinopathy Study (ETDRS) charts.[18] Lighthouse distance VA charts (Sloan letters), High-Contrast Bailey-Lovie Chart, HOTV, Landolt rings, LEA Symbols Chart.[19]
Figure 2: ETDRS chart (log MAR chart) https://en.wikipedia.org/wiki/File: ETDRS_Chart_R.svg. MAR: Minimum angle of resolution

Click here to view


When the top line cannot be seen from 3m; the test distance should be reduced to 1.5m or even 1m and then to 0.5 m till the patient can read a couple of letters or lines. The VA is then recorded as the smallest line seen (e.g., 0.5/24). A correction factor of 0.3 should be added to the Log score when the distance is halved. When VA falls below that the examiner should test for hand movement and perception of light. Distance VA should also be measured with multiple pinholes to assess possible refractive error. Fixation should be assessed as eccentric fixation could indicate the presence of central field loss and missing letters/symbols could indicate the presence of a visual field loss.

Near visual acuity testing

Graded continuous text materials will provide a more accurate measure of reading ability than single optotypes measure. Some examples are Lighthouse “NUMBER” card, Lighthouse Near VA Test Chart (Modified ETDRS with SloanLetters),[20] Lighthouse Continuous Text Card, LEA Symbols, and Minnesota LV reading chart (MNREAD) card.[21] They are calibrated in meter equivalents (M units), and these simplify the calculation of magnification. The reading distance in centimeters is the numerator. The print size in M units is denominator, for example, 40/4M. The smallest print read and the distance should be recorded. Magnification is prescribed to improve the reading distance, print size able to be read, or both an also overhead reading lamp to improve the contrast should be used.

Refraction

Refraction is an essential part of an LV examination to ensure the appropriate correction of refractive errors. It is important because the patient may appreciate a subjective increase in visual ability with glasses. Most LVDs are used in conjunction with refractive correction and the performance with LVDs may differ with and without glasses in cases of moderate refractive errors.

The basic step of retinoscopy has to be performed using any method. If the media is not clear retinoscopy is done at a closer distance may be 25 cm or 50 cm known as radical retinoscopy.

Just noticeable difference (JND) and Bracketing method: [12] JND is the amount of spherical lens change at which a change in clarity or blur is first noticed. Poorer the VA, the larger the JND.[22]

JND (for working distance 20 ft) = Snellen Acuity Denominator/100

For example: if VA is 20/200 the JND will be 2D and trial lenses of ± 1.00D would be compared with one another. The best sphere is calculated by bracketing around it with stronger and weaker lenses and therefore the refractive error can arrive quite accurately and reliably in patients with significant loss of sensitivity to blur.

In LV patients, phoropters are not advisable. The system of trial lenses and trial frames works better as patients with defective fields can use eccentric head or eye positions to read the chart. Still better are the large aperture full-frame trial lenses set. Objective readings help a great deal and avoid waste of time in the subjective assessment. In the case of high astigmatism, each meridian can be neutralized independently.

Contrast sensitivity

The minimum amount of contrast required for a person to see a target is known as the contrast threshold. The contrast sensitivity is just a reciprocal of the contrast threshold and it is the ability to detect objects at low contrast. As contrast sensitivity is usually affected in people with LV, it is an important test to help in the prescription of LV devices, so that lighting and other nonoptical devices can be considered. Contrast sensitivity is a better predictor of real-world functioning.[23] Some examples of contrast sensitivity test charts are – Pelli-Robson Chart, low-contrast VA charts (LCVA)[24] (Compared to high-contrast VA charts, LCVA shows a better correlation with reading, driving, or face recognition in several neurologic diseases),[25] Hiding Heidi charts, and functional contrast acuity test.

The information provided by the contrast sensitivity test often will help determine mono-ocularity versus binocularity, increased need for illumination, the necessity for occlusion, need for control of brightness and contrast, and the need for a higher than predicted add.

Color vision testing

Color vision testing indicates the level of difficulty a patient may have in performing tasks that require the processing of color information such as in activities of daily living (i.e., matching cloths, coloring, and recognizing traffic signals).

Common testing techniques are Ishihara, pseudoisochromatic color plates, Farnsworth dichotomous test (D–15), and Farnsworth Munsell 100 hue test. For blue-yellow dyschromatopsia, which is more common among patients with LV, color arrangement tests such as the Farnsworth 100 Hue and D-15 tests or the Wang and Wang color vision plates are more appropriate than the Ishihara test.[13],[26]

Visual fields

In LV, testing of VF helps in the following ways:

  • How the patient with LV may function in day-to-day activities?
  • How well the patient may respond to various rehabilitative approaches?
  • Whether the patient falls into the category of legal blindness?


Amsler Grid Charting-Amsler grid is the most commonly used test for evaluating the integrity of the central field. Some patients will have smaller scotomas when observing the grid binocularly than they have with each eye alone whereas another patient may have larger scotomas binocularly. This information helps in choosing LV devices for the individual.[27]

Peripheral visual fields may be tested by: confrontation, manual perimeters, automated perimeters.

For patients with LV, it is advisable to check for binocular visual fields (Esterman program available in the Humphrey Visual Field Analyzer),[28] which provides a better indication of the patient's difficulty in mobility, driving, and other daily living skills.[29]

Micro-perimetry

Microperimetry using the scanning laser ophthalmoscopy (SLO) technique helps in the identification of preferred retinal locus (PRL) and fixation stability in LV patients with central scotoma[30] [Figure 3]. Microperimeters map the pattern of a patient's response to light stimuli at various retinal points and superimpose that data on an image captured by SLO or fundus photography to precisely identify areas of impaired or preserved function. Eye-tracking technology corrects eye movement, allowing accurate testing and retesting of the same retinal point.[31]
Figure 3: Microperimetry images showing areas of scotoma as well as PRL. PRL: Preferred retinal locus

Click here to view


In patients with loss of central fixation, the nonfunctional fovea is replaced by eccentric locations in healthier retinal regions, called the PRL. Fixation characteristics and the PRL are important to perform activities of daily living. Most patients are unaware of where that spot is, so they have to move their heads around each time until they find it. This area can be detected by microperimetry and the patient can be taught to find the PRL quickly and use it efficiently. In some patients, the PRL is not in an appropriate place and must be moved to a location that is more suitable for the patient and has higher retinal sensitivity. Using the biofeedback feature of the microperimetry device, this area can be relocated to healthier retinal regions with PRL shifting exercises trained retinal locus.

Microperimetry is used in patients with LV due to age-related macular degeneration, retinitis pigmentosa, Stargardt disease, diabetic retinopathy, and glaucoma.[32]

Useful field of view testing

The test can be administered in about 15 min and is recommended for use as a screening measure in conjunction with a clinical examination of cognitive functioning or fitness to drive.[33] It is recommended for people who are age 55-year-old or older, who have suffered health problems that can cause deficits in thinking abilities (e.g., stroke, Alzheimer's disease, and head injury), who are concerned about their driving ability, and who have had multiple vehicle crashes.[34]

Glare testing

Glare is usually due to intraocular scattering of light and people having anterior segment pathology (involving cornea/iris or lens) face difficulty in presence of bright light.

The brightness acuity tester (BAT) can be used to subjectively determine the effect of glare on visual performance. While viewing through the aperture in the BAT and wearing the best subjective distance correction, the patient reads the distance ETDRS chart under low, medium, and high settings. The fellow eye needs to be occluded. If there is a decrease of two or more lines of VA, then it is interpreted as glare causing a significant reduction in visual performance in presence of bright light. The effect of filters to relieve glare can be subsequently tried.[35]

The clinician can also check objectively for the glare problem by observing-squeezing of lids, moving the head down, using the hand as a visor.

Ocular motility and binocular vision assessment

Ocular motility testing should be carefully evaluated. Patients with extreme tunnel vision may experience a breakdown in binocular vision. Hirschberg estimation and sensorimotor testing (e.g., worth four dot, stereo fly, and red lens test) can be used to assess binocular function and to determine the need or potential for binocular correction.

Ocular health examination

Another very important part of the LV examination is the ocular health examination which includes external examination, slit-lamp examination, intraocular pressures, and postdilated lens and fundus evaluation. These ensure that there are no treatable lesions that may require treatment or referral to another specialist.


  Functional Evaluation Top


The term functional vision impairment has more importance from a person's perspective as it prevents or causes difficulty in performing tasks or daily activities such as reading, driving, recognizing people's faces, telling colors apart, and watching television or computer screen. It is manifested by insufficient visual resolution, inadequate field of vision, and reduced contrast acuity which affects the QoL. Reading speed which is most crucial in LV patients can be assessed by International Reading Speed Texts[36] which has single-size text and the MNREAD test (Minnesota LV reading test) which has varying text sizes and this can indicate a patient's potential reading speed with an adaptive device.[37] MNREAD charts are usually used for near reading at a distance of 40 cm but they can be used for a distance closer than 40 cm for LV patients. The effect of LV on the QoL can be assessed by questionnaires as described earlier and this evaluation can point out the functional disability caused by visual impairment.

The assessment of functional vision in children can be performed by the LV kit from Barraga and Tobin.[38] The seven areas of skills assessed using this kit are:

  1. Awareness and attention to objects-Finding an object or target and looking at it (fixating) long enough to be aware of it or recognize it
  2. Control of eye movements-tracking is required to follow the movements of traffic, people, or objects (such as a ball)
  3. Control of eye movements–scanning. A low-vision person has to search around for a long time to find objects and it might be difficult to change from looking at near objects to looking for something further away
  4. Discrimination of objects-assessment is done on whether a person can discriminate between people and objects, recognize familiar objects, or recognize different or similar objects
  5. Discrimination of details to identify actions and match objects – Most learning occurs from visual awareness and imitation. Therefore, factors of distance, size, color, and contrast are very important
  6. Discrimination of details in pictures – to asses whether a person can recognize actions or Complex picture
  7. Identification and perception of patterns, numbers, and words– this is very important to know whether the person can discriminate between similar and different shapes and letters. It will help in making decisions on whether a person should use normal-size print, large print, LV devices, or may need braille.


The conclusion should be made on the following criteria-how easy or difficult the task was, the person's purview, behavior during the assessment, distance for each item, the time is taken to finish the task, for example, “quick,” “needed a long time” or “slow to respond,” “scanning slow andrandom,” LV devices were available and used.


  Vision Rehabilitation Top


LVDs play an important role in vision rehabilitation. The basic principle of all LV optical devices is to magnify. The basic principle behind LVDs is to alter the environmental perception through.[39]

  • Bigger brighter and blacker
  • Closer color and contrast.


LVD make use of either of these four or a combination of these types of magnifications.[40] They are:

Relative size

Enlargement of the size of the object, for example, large print textbooks.

Relative distance magnification

It is achieved by moving the object of regard close to the eye and subtending a larger image on the retina. The magnification is inversely proportional to the change from the original distance.

Angular magnification

It is the apparent change in the size of the object. This type of magnification is generally produced by magnifiers or telescopic systems.

Electro-optical magnification

This is produced by electronic magnification devices and computer software, which not only enlarges the objects but also increases the contrast.

The higher the magnification, the smaller the field of view and the closer the working distance, and the depth of field is also reduced. The selection of the device will thus, depend upon these factors and not only on the level of magnification targeted.[41]

Types of assistive devices

LVDs are basically of four types:[42],[43]

  1. Optical Devices-incorporating lenses to achieve optical magnification
  2. Nonoptical Devices or supplementary devices that do not use optical lenses
  3. Electronic Devices, using electronic/optical techniques that achieve magnification
  4. Complex Devices using advanced technologies-JAWS screen reading software converts a normal PC into a talking computer while MAGic 8.0 is screen magnification software. Other soft wares are Zoom and Voice Over app, Zoom Text, etc.


A multidisciplinary team approach is advised to combat the disability and psychological issues caused by vision loss. The ophthalmologist is a team leader and the patient is an active participant in the rehabilitation process. The rehabilitation team should provide continued opportunities for training and reinforcement, occupational rehabilitation as appropriate, hope, and lifestyle changes to patients whose lives have been significantly affected by vision loss.[44]


  Conclusion Top


LV is a relatively overlooked field in ophthalmology as compared to the magnitude of the problem. The preliminary step should be to sensitize the practitioners and create interest among them and thereby in-depth training. Medical Curriculum should be framed in such a way that each category can carry out its responsibility properly. Periodic refresher courses need to be arranged to update people on different developments in the field of LV. Success in combating the problem depends on awareness of the disease within the community. Various studies prove that awareness of refractive error and LV is very low not only globally but also among the people involved in eye care starting from the ophthalmologists to the paramedics, making it difficult for the individual patient to engage in preventive actions, diagnosis, or treatment. With optical and nonoptical devices, we can help people use their remaining eyesight optimally and continue to function routinely otherwise. LV rehabilitation is the only nonsurgical treatment modality for vision loss so extra attention needs to be given to this field in terms of increasing financial support to existing centers and eye health programs, increasing numbers of LV centers, making low-cost and high-quality LVDs available and lastly spreading awareness among the people and community for eye health.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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