SN6 SHORT NOTE 5M ★ High-yield

Describe low vision with its assessment and aids.

Ophthalmology · 3rd Professional

Low vision is visual impairment which cannot be corrected by spectacles, contact lenses, medical treatment or surgery, and which interferes with the performance of daily activities — but in which useful residual vision remains.
The emphasis is on what the person can still do, not on what has been lost.

Category (WHO / ICD)	Presenting visual acuity in the better eye
Mild or no impairment	6/12 or better
Moderate impairment	Worse than 6/12 to 6/18
Severe impairment	Worse than 6/18 to 6/60
Blindness	Worse than 3/60, or a visual field of less than 10 degrees around fixation
INDIA — the national definition of blindness	Presenting distance visual acuity less than 3/60 in the better eye, or a field of less than 10 degrees — the definition was revised in 2017 from 6/60 to 3/60 to align with the WHO criterion.

The distinction between low vision and blindness is functional, not numerical: a person with low vision has vision that can be used and enhanced, and the whole of low-vision practice consists in doing so

Assessment goes beyond acuity — distance and near acuity with a LogMAR chart at a shortened working distance; refraction, which is repeated carefully because even a small gain matters; contrast sensitivity, which often correlates with function better than acuity does; visual fields; glare and illumination preferences; and above all a functional history — what the person actually wants to do
The principle of magnification — all optical aids work by enlarging the retinal image, and there is an unavoidable trade-off: the greater the magnification, the smaller the field and the shorter the working distance. This is why the strongest aid is rarely the most useful

Aid	Use and limitation
Spectacle-mounted high plus lenses	Simple and hands-free; but the working distance becomes very short.
Hand and stand magnifiers	Familiar, cheap and well accepted; illuminated versions are better. Hand magnifiers need steady hands, and stand magnifiers suit tremor and arthritis
Telescopes (monocular and bioptic)	For distance — a bus number, a blackboard, a television. Small field and difficult when moving
Electronic magnifiers and CCTV	High magnification with a normal working distance, adjustable contrast and reverse polarity (white on black).
Smartphone and tablet features	Now the most widely used aids of all — magnification, zoom, contrast inversion, text-to-speech and optical character recognition, on a device the person already owns
Non-optical aids	Often the most valuable, and the most neglected: illumination (task lighting is the single most effective intervention), typoscopes and reading masks, large-print and bold-line materials, contrast enhancement in the home (a dark plate for light food, marked steps), tinted glasses and caps for glare, and talking watches and scales
Field expanders	Prisms and reversed telescopes for constricted fields, as in retinitis pigmentosa and hemianopia

Rehabilitation is multidisciplinary — the optometrist and low-vision specialist; orientation and mobility training including the white cane; occupational therapy and home assessment; braille and assistive technology; educational support and integrated schooling for children; vocational rehabilitation; and psychological support, since depression is common and consistently under-recognised
In India — the Rights of Persons with Disabilities Act 2016 recognises blindness and low vision as disabilities, with entitlements to a disability certificate, reservation in education and employment, concessions and pensions; and the National Programme for Control of Blindness and Visual Impairment includes low-vision services
Ask what the person wants to do, and prescribe for that task; a single goal achieved is worth more than a cabinet of unused devices

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