Low Vision

By Eyecare NG

Overview   |  Causes  |   Diagnosis   |   Management & Rehabilitation

Overview

Low vision is a condition in which one has significantly reduced vision that cannot be corrected or improved with regular treatment options (such as glasses, contact lenses, medications and surgery), and in which the daily activities of the person involved is significantly affected.

Based on visual acuity, low vision can be defined as a condition in which an individual’s best correctable visual acuity is 20/70 or worse in the better eye.

Functionally, once someone does not have enough vision to do what he usually does or need to do after all regular treatment options such as glasses, medications and surgery have been given; the person is said to have low vision. This normally manifest as difficulty reading, writing, recognising faces, watching television and driving.

Central vision loss, peripheral vision loss, poor vision at night (night blindness), hazy and blurred vision, glare and reduced contrast sensitivity are common in people with low vision. For these people to carry out daily activities and live better quality lives, any little vision they have needs to be maximized.

Low vision can affect both adults and children.

Causes

The following are some of the conditions that can cause low vision:

  • Cataract – Causes reduced blurry or cloudy vision and poor contrast sensitivity.
  • Macular degeneration – Affects central vision making it difficult for victims to read, write, recognise faces and drive. Contrast sensitivity is equally affected.
  • Glaucoma and other conditions that damage the optic nerve (e. g. optic atrophy) – Affects the peripheral or side vision resulting in tunnel vision and impaired navigation
  • Retinitis pigmentosa – Affects the peripheral vision and also causes night blindness.
  • Diabetic retinopathy – Affects both central, and peripheral vision and reduces contrast sensitivity.
  • Albinism – Causes generalised reduction in vision and increased sensitivity to light
  • Brain injury from conditions like stroke – Affects visual processing and interpretation. It can cause central and peripheral vision loss, reduced contract sensitivity, blurry vision, eye misalignment and more.
  • Eye cancers – Can lead to loss of both central and peripheral vision.
  • Retinopathy of prematurity – Leads to peripheral field loss.

Diagnosis

Diagnosis of low vision is made after a comprehensive eye examination. This includes detailed case history, visual acuity measurement, refraction, external and internal eye examination, visual field assessment and other supplemental tests that may be required.

If visual acuity cannot be improved after all possible treatment options ( glasses, contact lenses, medication and surgery) has been exhausted, a diagnosis of low vision is made.

Management and Rehabilitation

Since lost vision cannot be restored in low vision cases, management of low vision entails maximizing the existing vision a person has to help him/her perform daily activities and live a close to normal life as possible.

Low vision management is individualized and dependent on a holistic assessment of the person’s needs. It includes a low vision assessment, identification of appropriate low vision aids, and rehabilitative training (such as mobility training and training on the use of the optical aids).

Low vision assessment

Low vision assessment will typically include:

  • History taking to obtain information on previous treatment (such as surgeries, use of optical aids and medications), daily activities, needs and wants.
  • Visual acuity testing using special visual acuity charts designed for low vision assessment.
  • Low vision refraction using some low vision aids to determine the optical visual aid that meets the person’s needs.
  • Other tests such as the Amsler grid test (to assess central vision), contrast sensitivity, colour vision, glare test, and more as required.

Vision rehabilitation

Low vision rehabilitation is aimed at maximizing existing vision and this often requires multidisciplinary effort by professionals such as eye care practitioners, low vision specialists, occupational therapists, orientation and mobility specialists, social workers, psychologists or counsellors

Some of the techniques used to maximise functional vision in low vision include:

Use of vision aids that magnify object/prints or enhance their perception

Low vision aids include:

  • Optical low vision aids such as high plus spectacles (spectacle magnifies), hand magnifiers,  stand magnifiers,  telescopes and other optical aids designed to magnify objects so that they can be seen easily.
  • Non -optical aids such as talking items (such as talking watches and timers), large print materials (e.g. books, newspapers), gadgets  with large prints (like watches and  telephones), reading stand, reading slit, bold line papers and walking sticks (to detect obstruction in the alkway and prevent falls)
  • Electronic devices such as CCTV or video magnifiers, audio books and electronic books, smartphones, tablets and computers

Redesigning or reorganizing the person’s environment to maximize functional vision.

This may include:

  • Use of reading lights in addition to room lighting to enhance the clarity of prints on the reading materials.
  • Proper positioning of lighting and desk to avoid glare and shadows.
  • Installation of curtains/ blinds that help reduce glare from reflective surfaces by minimizing the amount of external light that gets into the room.
  • Increasing contrast between objects and their background to enhance visibility. E.g. White plate on a black tray, white switch on dark switch plate, stairway with contrasting colours and more.