What is Retinitis Pigmentosa?
Retinitis Pigmentosa is a genetically inherited disease involving the rod receptors, cone receptors, and retinal pigment epithelium of the retina. It can occur as a sporadic rare occurrence or it is inherited as an autosomal recessive, autosomal dominant or X-linked genetic disease.
What Happens in the Retina from Retinitis Pigmentosa?
Usually the genetic defect causes a mutation of the rhodopsin gene. This causes the death of the rod and cone receptors with a failure of the retinal epithelial pigment cells.
Symptoms of Retinitis Pigmentosa
People begin to notice vision problems at night since the disease starts affecting the rods first. This also leads to decreased side vision. In the end stages of Retinitis Pigmentosa the person develops tunnel vision. As Retinitis Pigmentosa progresses, the vision can decrease to the level of 20/200 or worse in many people.
Diagnosis of Retinitis Pigmentosa
The diagnosis of Retinitis Pigmentosa is made by the history of their vision loss, classic exam findings, and the ERG findings of decreased b-wave amplitudes and prolonged implicit times.
Eye Exam Findings of Retinitis Pigmentosa
In the anterior portion of the eye posterior cataracts occur commonly.
The retinal findings include the classic pigment clumping in a bone-spicule pattern more prominently in the mid peripheral retina. Attenuation of the blood vessels in the retina is another classic finding. A pale and waxy appearance of the optic nerve is another classic finding. The retinal findings are symmetrical. People are commonly near-sighted. They can develop cystic lesions in the macula.
Diagnostic Testing for Retinitis Pigmentosa
ERG (full field electroretinogram)
An ERG measures the electrical potential generated by the rods and cones of the retina after being stimulated by a light that is flashed into the eye. In the beginning, the ERG is reduced but in the late stages can be reduced to no response.
The visual field measures the amount of light detected by the entire retinal area. The visual defect first shows in the mid periphery and later can lead to a total loss of side vision resulting in tunnel vision.
This is a measurement of the photoreceptors and retinal pigment epithelial potential. It is not as sensitive as the ERG and is not used very much anymore for Retinitis Pigmentosa.
This measures the threshold of the rods during dark adaptation. It is delayed and the threshold is elevated in Retinitis Pigmentosa.
Genetic testing can be done to confirm the diagnosis.
Treatment of Retinitis Pigmentosa
There is no definite proven treatment for Retinitis Pigmentosa. Some studies have shown that taking vitamin A, lutein, and meals of oily fish may have some benefit.
Protecting the eyes from ultraviolet light is a good thing to do by wearing sunglasses outdoors.
Genetic counseling should be given to families with Retinitis Pigmentosa.
Retinitis Pigmentosa Disease Course
In general, the autosomal dominant inheritance form does the best, the autosomal recessive inheritance form is second, and the X-linked inheritance form does the worst with their vision.