Retinitis pigmentosa

Retinitis pigmentosa (RP) refers to a group of inherited disorders that cannot be prevented and that slowly leads to the degeneration of part of the retina, primarily the photoreceptors. There is no known cure for RP, which will eventually lead to blindness.

The retina lines the interior surface of the back of the eye. The retina is made up of several layers. One layer contains two types of photoreceptor cellsreferred to as the rods and cones. The cones are responsible for sharp, central vision and color vision and are primarily located in a small area of theretina called the fovea. The area surrounding the fovea contains the rods, which are necessary for peripheral (side) vision and night vision (scotopic vision). The rod and cone photoreceptors convert light into electrical impulsesand send the message to the brain via the optic nerve where the image of whatwe see is produced. Another layer of the retina, called the retinal pigmented epithelium (RPE), may also be affected in this disorder.

In RP, the photoreceptors (primarily the rods) begin to deteriorate and losetheir ability to function. Because the rods are primarily affected, it becomes harder to see in dim light, thus producing a loss of night vision. As the condition progresses, peripheral vision disappears, resulting in tunnel vision. The ability to see color is eventually lost. In the late stages of the disease, there is only a small area of central vision remaining. Eventually, thistoo is lost.

The first symptom of RP is a loss of night vision followed by a loss of peripheral vision, usually begin in early adolescents or young adults. Occasionally, the loss of the ability to see color occurs before the loss of peripheralvision. Other symptoms can include seeing twinkling lights or small flashes of lights.

When a person complains of a loss of night vision, a doctor will examine theinterior of the eye with an ophthalmoscope to determine if there are changesin the retina indicative of RP. However, the appearance of the retina is notenough for a diagnosis. There are other disorders that may give the retina asimilar appearance to RP. There are also other reasons someone may have nightblindness. For that reason, certain electrodiagnostic tests will be performed--either an electroretinogram (ERG) or an electro-oculogram (EOG); or a visual field examination, which can help determine if side vision is reduced.

There are no medications or surgery to treat this condition. Some doctors believe vitamins A and E will slightly slow the progression of the disease in some people. However, large doses of certain vitamins may be toxic and patientsshould speak to their doctors before taking certain supplements.

If a person with RP must be exposed to bright sunlight, some doctors recommend wearing dark glasses to reduce the effect on the retina. The glasses shouldprotect against ultraviolet (UV) and infrared (IR) rays. Dark tint alone will not protect the eyes. Patients should talk to their eye doctors about the correct lenses to wear outdoors.

Because there is no cure for RP, the patient should be monitored for visual function and counselled about low-vision aids (for example, field-expansion devices). Also, when expectant parents--or couples who wish to become pregnant--are related to anyone who has had RP, they should receive genetic counseling.

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