In these conditions the retina slowly degenerates losing its ability to transmit images to the brain. In advanced stages of the conditions, characteristic clumps of pigment appear in the retina. Often the first symptom is night blindness, followed by narrowing of side vision leading to 'tunnel' vision.
Retinitis pigmentosa (RP) is the name given to a group of genetic conditions of the retina, the light-sensitive tissue at the back of the eye. The retina converts light images to nerve signals and sends them to the brain.
The most sensitive part of the retina is small area of the central retina called the macula. The macula contains a few million specialised photoreceptors called cone cells - these work best in bright light levels and are used for reading, writing and to recognise colours. The rest of the retina, called the peripheral retina, is mostly made up of A type of photoreceptor called rod cells. Rod cells enable us to see when light is dim and provide peripheral vision.
Medical text written November 2012 by Professor AT Moore, Professor of Ophthalmology, UCL Institute of Ophthalmology and Moorfields Eye Hospital, London, UK.
What are the symptoms?
What are the causes?
All cases of RP are inherited and a large number of genes have been implicated in causing the condition. In most cases, the peripheral rod cells are affected first with the central cone cells being affected later.
RP can also be associated with other problems such as hearing loss. These rare conditions are referred to as RP syndromes, for example, Usher syndrome.
How is it diagnosed?
A number of tests can be used to diagnose RP:
- retina examination - eye drops are given to dilate the pupils so the retina can be viewed easily
- retinal photographs and specialised retinal imaging - a photograph may be taken of the retina using a special camera.
- visual field test - this checks whether peripheral vision has been affected. The person looks straight ahead at a particular point in the bowl-shaped screen in a darkened room and then dim lights or a moving light are presented in the peripheral field. Each time a spot dots of light is seen the person being tested clicks a button
- colour vision tests - the person will be asked to look at a booklet that shows numbers composed of different coloured dots
- electro-diagnostic tests - the electrical activity of the retina is measured under different lighting conditions and this identifies layers of the retina that are not working properly. This involves having a small wire or thread placed on the eye lids and another on the scalp whilst having watching flashing lights.
How is it treated?
Treatment focuses on managing the symptoms of RP. Wearing sunglasses to protect the retina from ultraviolet light may help preserve vision. For those patients who have poor central vision it can help to see a low-vision specialist, who can help people adapt to vision loss. Regular visits to an eye care specialist, who can detect cataracts or swelling of the retina - both of which can be treated - is essential.
Some studies have suggested that treatment with antioxidants (such as high doses of vitamin A palmitate) may slow the disease but high doses of vitamin A can cause side effects. Several clinical trials are in progress to investigate other dietary treatments for RP, including the omega-3 fatty acid, docosahexaenoic acid (DHA).
Other new treatments such as the use of biological growth factors and gene replacement therapy are being evaluated in clinical trials. Microchip implants that are placed under or on the surface of the retina and stimulate the nerve cells directly are in the early stages of development for treating blindness associated with RP and other serious eye conditions.
Inheritance patterns and prenatal diagnosis
For RP inheritance may be autosomal dominant, autosomal recessive or Inheritance of RP may be autosomal dominant, autosomal recessive or X-linked. Affected families should be referred to a genetics centre for information and support
Prenatal diagnosis is now possible in some forms of RP and other inherited retinal disorders, but only in those cases where the genetic change causing the condition has been identified.
Is there support?
RP Fighting Blindness
The Society is a Registered Charity in England and Wales No. 1153851. It provides information and support to people with retinitis pigmentosa (RP) and their families, and anyone with an interest in the condition. The Organisation has a network of local groups across the UK.
Group details last updated December 2014.