Retinitis pigmentosa (RP) is a group of inherited diseases that cause degeneration of the rods and cones of the retina.
Although the disease name includes the suffix “itis”, which generally indicates an inflammation, no infection or inflammation is associated with these disorders.
RP first affects the rods and as they are destroyed, vision in low light is decreased, and peripheral vision constricts. As the disease progresses, the cones are affected and central vision is lost. Although a hereditary condition, RP rarely accompanies other diseases. When accompanied by a serious hearing loss, the disorder is termed Usher’s syndrome.
There are several types of RP:
- Congenital RP, or Leber’s congenital amaurosis, is apparent at birth or in infancy. This is a rare disease causing a steady, progressive loss of sight.
- Recessive RP is passed to the child of two individuals who carry the gene but who may not have the disorder themselves. There is a 25% probability that a child (male or female) of two carriers will have RP.
- Dominant RP is passed to a child of one affected parent and one unaffected parent. With each pregnancy, there is a 50/50 probability that each child (male or female) will inherit the disease. Unaffected children usually will not pass on the disease to their children. Three genes thought to cause dominant RP have been discovered.
- Sex-linked RP is passed to a child by the mother, who is the carrier. Sons of a female carrier and an unaffected male have a 50/50 probability of being carriers but will not inherit the disease. Severity varies with the individual. The genetic cause and inheritance pattern is unknown. Research is being conducted to investigate new mutations as they appear with each generation.
The most common symptom of RP is night blindness or difficulty seeing in dim light. There may be a progressive loss of peripheral vision, resulting in tunnel vision. As the disease progresses, the individual may experience a loss of central vision. Many individuals may develop cataracts, or opaque sections on the lens of the eye.
Some may experience complete blindness but most will retain some limited vision. In most cases, the onset of RP is during childhood or early adolescence, but it is not easily diagnosed. Congenital, recessive, and disease-related types of the disease tend to be more severe than dominant RP.
Often, during an ophthalmologic exam, a change in the appearance of the retina may indicate RP but such other tests as an electroretinogram (ERG) may be necessary to confirm the diagnosis. An ERG measures the electrical activity of the retina when exposed to light stimulus. Drops are first placed in the eyes to dilate the pupils.
Anesthetic drops are administered to the eye just before a contact lens attached to electrodes is placed on the cornea of the eye. The electrodes record the responses of the retina as lights are flashed in both dark and light environmental conditions.
There is no cure or treatment for retinitis pigmentosa (RP). Vitamin A therapy, topical treatment with DMSO, and light deprivation have been investigated as cures, but results have not been as promising. Research thought to be the most promising involves nutritional therapy, retinal cell transplantaion, and gene therapy.
Some have been helped with vitamins A and E because RP is sometimes associated with a number of lipid disorders in which the body is unable to process certain fats. Taking the vitamins has slowed down or even stopped the spread of RP in some cases while others have shown no improvement.
