Spotlight on Retinitis Pigmentosa
What is it?
Retinitis Pigmentosa (RP) is the name given to a group of conditions that affect the rods and/or cones of the retina and thus light perception. RP is hereditary and is a degenerative condition.
The cells that make up the retina are cones and rods. There are far more rods and these make up the peripheral vision. These are the cells mostly affected by RP. Usually the rods are the first cells to be affected with the cones (central vision) affected at late stages of the disease.
What are the symptoms and signs?
Signs of RP usually begin to show in children but may also appear at later ages, with common symptoms including:
- Problems with vision at night and when lights are dim.
- Loss of peripheral vision, that is, the vision at the edges of view, which progressively leads to tunnel vision (when only the centre of the vision remains).
- Sensitivity to light (photophobia)
- Problems with colour vision
- Problems with adjusting from dark to light areas.
How is it diagnosed?
Tests to diagnosis RP include:
- Image of the fundus will show black spots around the periphery (see image).
- Visual field test (as mentioned in the previous post, where you stare at a dot in the middle and click the button when you see a dot/flash) which will show ‘blind spots’ usually in the periphery.
- Electrophysiology study, as mentioned in the previous post here, uses electrodes placed on the head and eyes in various conditions to analyse electrical signals.
- Genetic testing can be performed although there are a great number of possible contributing genes and a test can be costly and timely unless a gene is suspected, for example another family member has the condition and their gene mutation is known.
How common is it?
There is no definite figure for Australians affected by RP although the estimate is 1 in 3000 people.
What is the cause?
RP is a hereditary condition caused by a gene problem. The number of genes identified that lead to this condition are in excess of 100.
RP may be a recessive condition, where both parents are carriers but do not exhibit symptoms. Both genes, one from each parent, need to be inherited for the condition to manifest. This means there is a 25% chance if both parents are carriers. This is the most common form.
RP can also be a dominant condition, whereby one parent carries the gene and is also affected by the condition. The chance of inheriting the condition is higher, at 50%.
The rarest form of RP is X-linked recessive where the mother is a carrier and has a 50% chance of passing the condition on to a son only.
How is it treated?
As with most other inherited retinal diseases, there is no current treatment for RP. There are numerous clinical trials currently being conducted around the world which may lead to a treatment in the future. There are also other potential options such a retinal implants and bionic eyes.
What is the prognosis?
The progression of RP is different for each person and this means the prognosis can vary significantly. The age of onset, stages and severity of the disease can also vary. The following are potential outcomes of the condition:
- Only peripheral vision affected: A person may lose their peripheral vision and, depending on severity of the disease, may become legally blind. Central vision remains intact.
- Peripheral and some acuity (central vision) affected: This case leaves little or no peripheral vision and due to other RP disease factors there is less ‘crisp’ vision resulting in fogginess or blurriness. Shapes and objects may still be recognisable, reading managed with significant assistance but there is a lack of detail vision.
- Peripheral and severe central vision loss: This results in no peripheral vision, some light and colour perception or complete darkness.