Pigmentary retinitis

Pigmentary retinitis pigmentosa, also known as PR, develops as a result of certain genetic disorders that cause cells in the retina to break down. The retina is located at the back of the eye and is responsible for converting light into signals for the brain to perceive, thus enabling us to see. When these photoreceptor cells in the retina begin to degenerate, a person with retinitis pigmentosa sees a gradual deterioration in vision, usually causing difficulties in peripheral and night vision.

The first symptoms of retinitis pigmentosa usually appear between the ages of 10 and 40, but can occur in younger children if both eyes are affected. This age range, in which retinitis pigmentosa can develop at any time, can make it difficult to predict the extent and timing of visual deterioration.

Symptoms of retinitis pigmentosa usually start with poor night vision, as the cells responsible for seeing in low light stop working. In most cases, it takes us about 20 minutes to adjust to low light, but in PR it can take much longer or not at all. Eventually, you may be diagnosed with “night blindness”, which is likely to restrict you to being able to drive only during the day.

As retinitis pigmentosa progresses, the columellae (cells that respond to light) stop working. The columellae are needed for peripheral vision – what you can see at the edges of your field of vision. The vision caused by the loss of the columellae is called ‘tunnel vision’, where it becomes difficult to see the sides, top and bottom of an image when looking straight ahead.

Although rare, people with retinitis pigmentosa can also lose their central vision, making it difficult to concentrate on small tasks like reading.

Most people with retinitis pigmentosa inherit it from their parents. There are several genetic disorders that cause retinitis pigmentosa. These genetic disorders affect the genes responsible for making the proteins needed by the photoreceptor cells in the retina. When this protein is missing or damaged, the photoreceptor cells stop functioning and begin to die.

There are three main ways in which retinitis pigmentosa can be passed from parent to child. In some cases, a person can be a carrier without having the disease himself:

• Autosomal recessive inheritance – caused by two copies of the mutated gene because both parents are carriers. It is possible that the child is either a carrier or develops the disorder. However, the child’s health may not be affected at all.

• Autosomal dominant inheritance – caused by a gene mutation in one parent. There is a 1 in 2 chance that a child will inherit the disorder and develop retinitis pigmentosa.

• X-linked inheritance – if the mother has the PR gene linked to the X chromosome, there is a 1 in 2 chance that the son will develop PR and an equal chance that the daughter will be a PR carrier.

One of the main things to remember when diagnosing PR is to tell your eye specialist if you have a family history of the disease. This will mean that the eye specialist will need to examine your retina more closely during the examination.

In some cases, the eye specialist may identify specific signs in the back of the eye, on the retina, that indicate PR. A visual field test can also be used to assess the function of the peripheral retina and check for visual defects.

If your eye specialist detects any signs of retinitis pigmentosa, he or she will refer you to an ophthalmologist – an eye doctor – who will carry out further tests, including an assessment of the electrical signals sent to the brain and a PR genetic test.

Once a person has been diagnosed with retinitis pigmentosa, their condition is closely monitored and they are informed of any new treatments.