A person may be defined as having low vision if their sight cannot be corrected with conventional spectacles or contact lenses to the standard measurement of 6/6 (20/20). If their vision is significantly reduced or their field of view severely restricted then they may be eligible for registration as partially sighted or blind. Only a small minority of those registered blind have no sight at all. However, the degree of visual loss has no direct correlation to the problems each individual experiences.
There are diverse causes of low vision. The condition may be congenital/acquired, static/progressive/fluctuating, permanent/temporary. Loss of vision may be peripheral, central or both and there may be associated difficulties such as poor adaptation moving between light to dark areas, worse vision in bright or low light levels. Individuals may have other health or age-related problems.
The purpose of this entry is to outline the range of aids available to assist low vision patients to make the most of their remaining sight. None of these aids replicate the function of normal eyesight. Many tactile and audio aids are also available, but these will not be detailed here. Ideally every patient should be assessed in a well resourced low vision clinic (usually associated with a hospital eye department) where optical aids may be loaned to patients through the NHS. They should also have access to support from specialist social, employment or educational services with a view to provision of other aids and benefits. Unfortunately these facilities are insufficiently widespread for all patients to obtain optimum benefit. Purchases should not be made without professional assessment or at the very least, trying out the aid for its intended purpose.
After assessment for the most suitable aids, the key to success is patient motivation; an acceptance of their visual situation and determination to carry out desired tasks taking account of the limitations of the aids used.
There are some relatively simple ways to make visual tasks easier.
Firstly, the task should be well illuminated. Many patients find a halogen lamp, fluorescent or daylight bulb particularly helpful. An ordinary tungsten lamp may be too hot for comfort as the lamp will need to be positioned close to the user. Lamps should be shaded and directed so as to illuminate the area viewed but not such that stray light reaches the eyes.
Shading the eyes by using a sports eyeshade or a hat with a brim may be more helpful when outdoors than using sunglasses alone.
Contrast is very important. This can be improved by placing dark objects against a light background and vice versa (when preparing food or eating). Writing will be easier to read if a black fibre pen is used (rather than eg pencil) with good spacing between lines of text.
A ruler or piece of card may be useful to define the area viewed and is also used to block out distracting surroundings or mark the beginning of the line.
Television - sit closer. This is not harmful although other watchers may object if their view is blocked! Any object brought near will appear larger even if still not well defined. When central vision is affected, the view may appear clearer if the sight is directed off centre. This applies to other situations as well.
Photocopiers or scanners may be used to enlarge and enhance the contrast of pictures or text.
Broadly these can be divided into three categories: hand-held aids, stand magnifiers and spectacle mounted aids.
In general, the larger the lens of the magnifier, the weaker it is. Large 'page' or screen magnifying sheets are not usually of much benefit. Because of the limited field of view permitted by magnifiers, reading is slower as it is difficult to scan ahead in the normal way of reading.
Hand-held magnifiers are mostly lightweight, easily portable and relatively inexpensive. They may also be self-illuminated or folding. However, practice and a steady hand are needed to hold them at the correct distance for objects to be in focus. This category also includes hand-held telescopes and binoculars which may be used to enhance distance vision, though only when stationary.
Stand magnifiers may sit directly on the material, thus having the advantage of setting the focus, but tend to be bulkier. The stand may be a table mount with the magnifier on an arm, leaving the hands free. This type of magnifier is usually fairly large, but of low power.
Spectacle mounted aids include both simple magnifying lenses and more complex telescopic units. These may be for either distance or near vision. They have the advantage of leaving the hands free for practical tasks, but have a limited field of view and a critical close working distance (often extremely close). Also telescopic aids are more conspicuous - some patients dislike the cosmetic appearance, particularly for use in public.
Closed circuit televisions provide a more sophisticated option for near vision, but they are expensive. The matter to be looked at is placed under a camera and the magnified image is viewed on a screen. Print can be reversed to white on black (and sometimes other colour combinations). Other facilities may include underlining, creating a variable size window, zoom magnification and viewing distant objects.
A slightly less expensive option is either a camera that can be linked to an ordinary television or a digital system, also plugged into a television, using a control similar to a computer mouse to scan across material. There are a range of products available.
With computers, a wealth of new technology has become available. Standard operating systems usually incorporate the capability to tailor the view with enlarged fonts, contrast and colour adjustment. There are also specialist software packages which provide greater scope for magnification.
These electronic aids have the disadvantage of being relatively bulky and not easily portable. Other gadgets are being developed and tested which are head borne eg, Ocutech, NuVision, Nomad. Only a few patients as yet have achieved much success with these.
Other developments and such as ocular implantation of microchips are still very much in their infancy.