Retinitis pigmentosa (RP) is a rare, inherited disease that causes degeneration of the rod photoreceptors in the retina. The rods are the light-sensitive retinal cells responsible for vision in dim lighting environments and peripheral (or side) vision. According to the National Eye Institute, retinitis pigmentosa affects about 1 in 4,000 people worldwide.
Symptoms of RP
There are two hallmark symptoms associated with RP. The first symptom is a gradual decrease in night vision. It is difficult for the eyes to adjust in dark or dim lighting. This is followed by peripheral vision loss. As peripheral vision decreases, the visual field can eventually narrow to tunnel vision. Some people may have a small island of peripheral vision remaining, which can sometimes be utilized after vision rehabilitation training. Blindness can also occur late in the disease.
Causes of RP
Retinitis pigmentosa is caused by mutations to the genes that control protein production within the cells of the retina. It is a genetically inherited disease with multiple inheritance patterns: dominant, recessive, and X-linked. When RP is associated with the dominant gene, symptoms are more likely to be apparent in a person’s 40s. When inherited through a recessive gene, the symptoms are usually more severe and present in a person’s 20s. Initial symptoms may start mildly during adolescence and slowly worsen as the disease progresses.
Several tests are required to make a definitive diagnosis of RP. A dilated eye exam will reveal abnormal pigment deposits in the retina. The pigment starts at the peripheral retina and gradually spreads towards the central retina as the disease progresses. A visual field test is then used to determine if peripheral vision has been affected. This plots a map of the person’s peripheral and central vision. If the dilated eye exam and visual field are suggestive of RP, an electroretinogram (ERG) is the next step for confirmation. An ERG is used to measure the electrical activity of the retinal cells. Diagnosing RP is based on a decreased amount of electrical signals.
There is no cure for RP. Several companies are developing retinal implants to help restore sight. These tiny devices are implanted into the retina and transmit the electrical signals to the optic nerve. The implants do not provide normal, clear vision, but rather help the individual locate light sources and large objects. Other studies suggest high doses of vitamin A can help slow the progression of RP, however, this may not be suitable for every case of RP.
Low vision aids, such as telescopes and other lenses, are excellent resources for utilizing the remaining vision. Visual rehabilitation can help train individuals with RP on how to function with vision loss. Support groups are also available for those with decreased vision and any parent or caretaker of a person with vision loss.