Vision experiments

Background theory

Macular degeneration isn't a single eye disease but is the collective term to group together a set of chronic, degenerative eye diseases of the retina; the sensing surface of the eye. It is also known as age-related macular degeneration (AMD or ARMD) in keeping with the fact that it mostly arises in people aged 50 or older. There are other risk factors that play a role too: smoking, being overweight, eating an unhealthy diet or having vascular problems like high cholesterol or diabetes.

In all forms of this disease, there is a progressive loss of central vision, leaving the peripheral or side vision intact. Central vision primarily detects colour and fine detail (acuity) – for example, if you look straight ahead, it's difficult to know the colours of objects off the side or what they are.

Because of this effect, AMD/ARMD affects the ability to read, drive, recognise faces and perform activities that require detailed vision.

It is caused by damage to the nerves in your eye. The early and intermediate stage of AMD is caused by the progressive build-up of waste material called drusen under the retina. Generally, there is no major impact on vision, although some people with the later stage may notice changes to their central vision. From these stages, progression can occur to the late stage, when vision becomes impaired, but this is often idiosyncratic for each eye so that the rates can differ. In the late stage, there are two main types of AMD:

• Dry (atrophic) AMD – this kind of AMD, the most common kind, develops slowly. Hence, the loss of sight is slow and gradual from slight to severe central vision loss. It is caused by the gradual atrophy (loss) of retinal cells.
• Wet (neovascular) AMD – this type happens when abnormal and fragile blood vessels grow under the macula, and then proceed to leak blood and fluid under the retina. It is the most serious kind and develops very quickly, often resulting in a rapid loss of central vision. Loss of vision in one eye may go unnoticed if sight in the other eye is good. This is a serious and permanent stage for which there is no cure.

Amsler grid test

An Amsler grid test is sometimes used to detect vision problems resulting from damage to the macula.

Instructions:

1. Position yourself at eye level about 50cm away from the image.
2. Put on your reading glasses and cover one eye.
3. Look directly at the black dot.
4. Keeping your gaze fixed, try to see if any lines are distorted or missing. Take note of any distortions and their location.
5. Repeat the test with the other eye.

Macular degeneration simulation