Retinitis pigmentosa
Overview
Retinitis pigmentosa (RP) is a group of rare, genetic disorders that involve a breakdown and loss of cells in the retina—which is the light sensitive tissue that lines the back of the eye. Common symptoms include difficulty seeing at night and a loss of side (peripheral) vision.
Causes
Retinitis pigmentosa is caused by mutations in more than 50 genes. These genes carry the instructions for making proteins that are needed in cells within the retina, called photoreceptor cells. Some of these genes carry instructions for making proteins necessary for the structure and function of the photoreceptors. Others carry instructions for proteins that are involved in the function of the retinal pigment epithelium, which is a layer of cells that supports the photoreceptors.
Symptoms
The first symptom of retinitis pigmentosa, usually noticed in childhood, is decreased night vision (nyctalopia), which can make it difficult to navigate in low light. Later, the disease causes blind spots to develop in the side (peripheral) vision. Over time, these blind spots merge to produce tunnel vision (loss of all peripheral vision). In the advanced stages of the disease, individuals are often legally blind.
Diagnosis
The diagnosis of retinitis pigmentosa relies on documentation of progressive loss in photoreceptor function by electroretinography (ERG) and visual field testing. The mode of inheritance of RP is determined by family history. At least 35 different genes or loci are known to cause "nonsyndromic RP" (RP that is not the result of another disease or part of a wider syndrome).
Treatment
There is currently no cure for retinitis pigmentosa, but the progression of the disease can be reduced by the daily intake of 15000 IU (equivalent to 4.5 mg) of vitamin A palmitate. However, taking high doses of vitamin A can cause health problems, including liver damage and increased pressure on the brain.
Research
Research into treatments for retinitis pigmentosa are ongoing and include gene therapy, stem cell therapy, and retinal implants. A successful treatment could not only save sight for those who would otherwise suffer from blindness due to retinitis pigmentosa, but it could also provide important clues for treating other vision disorders.