Low Vision

Low vision describes the level of vision between being fully sighted and totally blind. Having low vision upsets a person’s ability to carry out many of the daily tasks for which vision is essential.

Fortunately, the remaining vision can often be used effectively with the help of magnifiers and other vision aids. Many optometrists specialise in helping people with moderate and severe vision impairment and can help patients make the best use of their remaining vision.

What is low vision?

Low vision is clinically defined as a specific range of visual acuity, which is the ability to read letters on an eye testing chart of decreasing size. Low vision may also be determined by a person’s impaired ability to detect objects in their side or peripheral vision, and a high sensitivity to medium and low contrast. Practical definitions state that a person has low vision when, as a result of an eye condition or disease, he or she cannot perform vision tasks that ordinarily are not difficult, or they do not meet the vision standard for driving.

What causes low vision?

People of any age can have low vision. Infants and children can be born with inherited or developmental anomalies of the eyes that cause low vision. About 90 per cent of children with low vision have a stable ocular condition so their vision is unlikely to deteriorate in working adulthood. Low vision care for these children offers lifelong benefits.

Young adults might suffer from inherited conditions that manifest later in life. A loss of central vision occurs in macular dystrophies such as Stargardt’s disease, while peripheral vision loss is progressive in retinitis pigmentosa. General health conditions such as diabetes can lead to retinal complications and cataracts.

Low vision is most common in older people. Macular degeneration and glaucoma are common conditions that are sometimes unable to be cured with medical treatment, and medical conditions such as strokes and brain tumours can rob a person of half their visual field. Optometrists provide advice on managing visual field losses.

What are the effects of low vision?

Loss of clear vision is one consequence of many low vision conditions. If light is not transmitted sharply into the eye, or if the macula, the central and most sensitive part of the retina, is poorly developed or diseased, detailed vision will be poor and people will find it hard to see faces clearly, watch television, read print and manage other day-to-day tasks.

Loss of side or peripheral vision has the opposite effect. Although detailed vision may be relatively unaffected, the vision we need for walking around safely may be lost. People trip or bump into objects and fail to see obstacles just out of their straight-ahead view, and driving becomes illegal and crossing roads dangerous.

Poor contrast vision, as well as developing with old age, occurs in many eye conditions. Subtle shades of colour and light and dark become difficult or impossible to discern. Vision becomes more difficult at night or in bright sunlight, sometimes to the point of extreme discomfort.

How is low vision treated?

Optometrists are specially trained to measure vision accurately; they can assess the magnification or other requirements a person with low vision needs to perform specific day-to-day tasks.

There are several options available to make seeing easier:

  • Making things bigger, such as large print books or direction signs.
  • Stronger than usual reading glasses can be prescribed to enlarge the image inside the eye and make objects easier to see.
  • Brighter lighting can improve a person’s sensitivity to objects of low contrast, making subtle shades of grey and colour more obvious.
  • Bolder colours give objects better contrast against their background, for example painting the edges of steps to make them more visible and reduce the risk of falling.

Task-specific optical magnifiers are also helpful; the correct magnifier for one task may not be appropriate for another, but these can be compact and convenient.

Low vision aids can be simple, such as large print books, clocks with large numbers or plastic templates to help people fill out forms. Mobility aids, such as a long cane, can help a person with low vision maintain their independence.

An optometrist can also refer patients to a local vision support agency whose rehabilitation staff can visit patients’ homes and help them make improvements to their environment to make seeing easier.

Are there special magnifying aids to help?

Depending on the distance of a vision task, there are various low vision aids that might be needed. Magnifiers are prescribed for the specific task as well as the level of sight loss and the fineness of detail the person needs to see.

Distance tasks

  • Further than two metres away.
  • Include driving, and watching television, sports and stage performances.
  • Optical devices to assist distance vision include spectacles for correcting out-of-focus errors, suitable tinted spectacles to manage glare, and binoculars or small telescopes.

Intermediate or middle-range tasks

  • Between two metres and 50 centimetres from the face.
  • Include many day-to-day activities such as playing cards, reading music, cooking and workshop activities.
  • If details of the task can be enlarged or brought much closer, special vision aids might not be required.

Near tasks

  • Those closer than 50 centimetres, usually well within arm’s reach.
  • Hand-held and stand magnifying lenses, often with battery or mains operated lights built-in, stronger reading glasses and very bright task lighting are useful options for this range.

How much do magnifiers cost?

Low vision magnifiers vary in quality and price; ordinary magnifiers bought from hardware and novelty stores have simple lenses of low power, while better quality magnifiers use the best optical materials with computer-designed lenses to provide wide images with little or no edge distortion.

The chosen quality may be the difference between being able to read comfortably or just managing to read a few sentences one or two letters at a time.

How does technology aid people with low vision?

Sometimes an optical magnifier cannot provide enough image enlargement. More advanced technology for dealing with low vision includes:

  • Tiny television cameras held close to a page enable greatly enlarged images to be viewed on an ordinary television screen or computer monitor.
  • Electronic magnification also allows us to reverse or enhance the contrast of print, accentuate colours and even change the way print is presented.
  • Printed text can be rearranged to scroll up the screen automatically, move across the screen in a single line or flash centrally on the screen as individual words.
  • Some text can be converted into speech by a scanning computer and text can also be converted into Braille (patterns of raised dots representing individual letters).

Whatever the level of vision, your optometrist is the first person to ask for advice. After exploring the need for conventional optical treatment, optometrists consider the more complex or unusual management strategies and will refer patients for specialist medical, optical or rehabilitation advice when necessary.

What rehabilitation and community support is available?

Your optometrist can refer you to obtain welfare and employment counselling and advice regarding pensions and other benefits. Many agencies have local support groups of people who share experiences and ideas about coping with vision loss. Referral to optometrists who specialise in prescribing complex or high-level optical devices is also available.