Eye Diseases

Retinis Pigmentosa (Information furnished by the Foundation Fighting Blindness)

What is RP?

Retinitis Pigmentosa (RP) is the name given to a group of degenerative diseases of the retina. The retina, at the back of the eye, is a thin sheet of interconnected nerve cells including the light sensitive cells (rods and cones). It is here that light is converted into electrical signals to the brain where "seeing" takes place. In RP the rod and cone cells degenerate. Depending on the type of RP, the rate of progression varies.

What are the symptoms?

Usually the rod cells are the first to be affected. They are concentrated away from the centre of vision in the retina and are responsible for seeing in dim light. Thus, one of the earliest symptoms is often night blindness followed by loss of peripheral vision leading to "tunnel vision".

Cone cells in contrast are concentrated in the centre of the retina and are responsible for brightly detailed colour vision. In cases where the cone cells degenerate first, central vision becomes blurred and loss of colour perception occurs. Peripheral vision is initially retained.

Although the majority of people with RP do not suffer from associated disabilities, it does happen. Deafness associated with RP in a condition known as Usher syndrome is one such disability.

Who does it affect?

The symptoms of RP may occur at any age but most commonly they appear in young adults. Generally speaking, the earlier the disease begins, the more severe the symptoms. Occasionally the disease is present at birth and can be diagnosed with appropriate testing at that time. RP is recognized as one of the most common inherited causes of blindness in people between the ages of 20 and 60.

How quickly does it progress?

Most patients have very gradual progression of symptoms, often over many years or decades. Generally, when other members of a family are affected, the rate of vision loss is usually similar. Different forms of RP advance at different rates.

Can the progress be halted and is there a cure?

Besides high doses of Vitamin A that have been shown to provide some benefit for RP patients, there is no known way to halt the degeneration of the retina or cure the disease. Transplants of the retina are not possible at this time and there is no convincing scientific evidence to demonstrate benefit from any treatment methods currently available. There are, however, a number of areas currently being researched that may demonstrate potential for treatment.

How is it diagnosed?

Whenever RP is suspected or is a concern, a person should be evaluated by an ophthalmologist (medical eye doctor). The disease is usually most difficult to diagnose in the earliest stages. Depending on the stage and type of the disorder, tests of vision function such as visual field, dark adaptation and electroretinograms (ERG) are made to determine the precise state of the retina.

How is it transmitted?

Fifty per cent of cases of RP are sporadic with no previous family history. The cause of these cases cannot be explained. Other cases are inherited and fall into three main groups:

Autosomal recessive forms of the disease occur when both parents are unaffected carriers of the same defective gene. The chance of a child of theirs being affected is 1 in 4 (the affected child must inherit the defective gene from each parent). The chances of a parent having an unaffected child who, like them, would be a carrier of the defective gene is 1 in 2. The chance of such parents having a child completely free of the RP gene is 1 in 4.

Autosomal dominant forms of the disease are characterized by expression of the disease in either males or females when only a single copy of the gene is defective. In such cases, it is typical that one of the parents is affected by the disease. Since the affected parent has one normal and one defective gene, the chance is 1 in 2 of any given offspring being affected by the disease.

X-linked (or gender linked) recessive forms occur in offspring in two ways. The fathers can be affected or mothers can be carriers of the defective gene. If the father is affected, all sons will be unaffected and all daughters will be carriers. If the mother is the carrier, 1 in 2 sons will be affected and 1 in 2 daughters will be carriers.

How is the type determined?

Family history is the single most important factor to determine the type of RP. Family members should be examined by an ophthalmologist. For example, some female carriers of the X-linked form can be identified by slight pigmentary change or a golden reflex in the retina.

What action can be taken by those affected?

Those affected by RP should seek the best information available from ophthalmologists about their particular condition. Depending on the condition, further action may be appropriate in the field of education, training and family planning.