What is Retinitis Pigmentosa?
Retinitis Pigmentosa (RP) is the name given to a group of inherited diseases that affect the retina. They are characterized by a gradual breakdown and degeneration of photoreceptor cells, which results in a progressive loss of vision.
RP causes degeneration of the retina, a delicate tissue composed of several cell layers that line the inside of the back of the eye and contain photoreceptor cells (rods and cones). The rods are concentrated outside the center of the retina, known as the macula, and are required for peripheral vision and for night vision. The cones are concentrated in the macula and are responsible for central and color vision. Together, rods and cones are the cells responsible for converting light into electrical impulses that transfer messages to the brain where “seeing” actually occurs.
The most common feature of all forms of RP is a gradual breakdown and degeneration of the rods and cones. Depending on which type of cell is predominantly affected, the symptoms vary.
If the individual has predominantly rod cell degeneration, night vision and peripheral vision will be affected initially. Night blindness, one of the earliest and most frequently symptoms of RP, is manifested not only in difficulty seeing at night, but also in dimly lit places. The loss of peripheral vision is often referred to as “tunnel vision.”
Individuals with predominantly cone cell degeneration may initially experience decreased central vision and loss of the ability to discriminate color before peripheral vision is diminished.
Symptoms of RP are most often recognized in adolescents and young adults, with progression of the disease usually continuing through the individual’s life. The rate of progression and degree of visual loss are variable.
Is Retinitis Pigmentosa inherited?
It is estimated that RP affects 100,000 individuals in the United States. It can be passed to succeeding family generations by one of three genetic inheritance patterns-autosomal dominant, autosomal recessive, or X-linked inheritance.
Each type of inheritance causes a different pattern of affected and unaffected family members. For example, unaffected parents could have both affected and unaffected children, as in families with the autosomal recessive type. In families with the autosomal dominant type, an affected parent could have both affected and unaffected children. In families with the X-linked type, only males will be affected, while females carry the genetic trait but do not experience serious vision loss.
It is very important to remember that because RP is an inherited disorder, it can potentially affect another member of a family. There are also isolated cases in which an individual appears to be the only member in the history of a family to have a retinal degeneration; however, these are probably cases of inherited RP as well. Individuals of an affected family may not experience the same intensity of symptoms and as a result may not recognize that they have RP and need medical consultation. If one member of a family is diagnosed with a hereditary retinal degeneration, it is strongly advised that all members of that family contact an ophthalmologist.
How is Retinitis Pigmentosa treated?
Intensive research is currently under way to discover the cause, prevention, and treatment of RP. At this time, researchers have identified a first step in managing RP. While not a cure, certain doses of vitamin A have been found to slow the progression of RP in some individuals. Contact your doctor or the RP Foundation for more information.
Researchers have found some of the genes that cause RP. It is now possible, in some families with X-linked RP or autosomal dominant RP, to perform a test on genetic material from blood and other cells to determine if members of an affected family have on or several RP genes. Although genetic testing may provide helpful diagnostic information in some types of RP, accurate diagnosis for all RP types must include special electrodiagnostic tests of retinal function, visual field testing and a thorough ophthalmologic examination. Genetic counseling should be obtained to assist in the interpretation of genetic test results as well as to define the risks of other family members or future offspring being affected.
As yet, there is no known cure for RP. Low vision aids, including optical, electronic and computer-based devices are available. Personal, educational, and vocational counseling, as well as adaptive training skills, job placement and income assistance is also available through community resources.