Retinitis pigmentosa (RP) is the name given to a group of diseases that cause progressive loss of vision. Approximately one in 4,000 people, or approximately 200,000 people in the U.S. have RP.
Retinitis pigmentosa is a progressive disorder that causes damage to the retina in the eye. The retina is the inside lining of the eye which contains special cells that are photoreceptors. When light strikes these cells, they convert the image to an electric signal that can be sent to the brain to be processed as vision. The photoreceptors in the middle of the retina are called cones and are responsible for seeing in color. The photoreceptors on the outer edges of the retina are called rods. Rods are responsible for seeing black and white images, and are more effective at seeing in low light.
RP Symptoms
In retinitis pigmentosa, the rods at the outer edges of the retina are most likely to be damaged, leading to a reduced ability to see in low light. Symptoms typically begin in early childhood and become progressively worse over time. Symptoms of RP include:
• Night blindness– Difficulty seeing in low light is often the first noticeable symptom of the disease.
• Light and glare problems – Patients with RP may complain that going into bright sunlight creates a “white-out” effect from the glare of the light.
• Tunnel vision – As cells in the retina are damaged, patients may lose peripheral vision, or may see the edges of their vision closing in, as though they are looking through a tunnel. Objects are visible in the center, but disappear at the edges of vision. On average, patients tend to lose about 5% from the edges of their visual field each year.
• Double vision – The brain processes overlapping signals from both eyes to create the images we see. As tunnel vision progresses, the signals from the eyes stop overlapping, which can cause an appearance of double vision.
• Cataracts – Patients with RP may develop cataracts, but misinterpret the loss of vision as one of the symptoms of RP. Surgery to remove cataracts may help reduce glare and problems with clarity of vision.
Help for RP Patients
Currently there is no effective treatment that can correct RP or stop the progression. Some studies indicate that treatment with antioxidants such as Vitamin A can be beneficial, but this has not been proven. Patients should continue to get their vision checked to watch for other problems that can accelerate the progression, including cataracts. Some patients benefit from the use of “reverse telescopes” which take a wide angle view and make it smaller to fit into the center of the patient’s field of vision. Care should be taken to make sure patients have adequate lighting at home to prevent tripping and falling. Patients experiencing problems with light glare may benefit from dark plum or amber tinted eyeglasses.
Retinitis pigmentosa is often a genetically inherited disease. In many cases, if one person in the family has RP, others will also have it. Family members should have their vision checked, and may benefit from genetic counseling to discuss the probability that future children may have the disorder. Although the disease is progressive, complete blindness is rare.
Sources:
Merck Manuals Online Library
Vision World Wide
National Institutes of Health: Medline Plus
University of Michigan Kellogg Eye Center