Retinitis Pigmentosa Guide Symptoms, Diagnosis and Treatment
Retinitis pigmentosa isn't one disease but rather a group of rare eye diseases, all of which cause the photoreceptors of the retina to degenerate. The retina is lining at the back of the eye which receives images and sends them via the optic nerve to the brain. There are two types of photoreceptors in the retina, called rods and cones, which react to light and make this process possible:
- Rods react to light and dark, but not color. There are approximately 120 million of them in the retina, concentrated in the outer region. Rods give us our night vision and peripheral vision.
- Cones are less sensitive than rods, but react to color. They are concentrated in the center of the retina, called the macula, and are responsible for our color vision and the sharpness of our central field of vision. There are much fewer cones in the eye than rods, only 6-7 million cones.
When these photoreceptors degenerate as a result of the disease, the result is permanent vision loss.
In 50% of patients, the retinitis pigmentosa is hereditary. There are over 100 possible genetic mutations thought to be responsible for the disease, some of which are X-linked, so while the disease does occur in both men and women, it affects males at a higher rate. Because the genes that cause retinitis pigmentosa are recessive, people can be carriers of a defective gene and pass it on to their children even if they do not have the disease themselves. The other 50% have no family history of the disease, and the cause is unknown in those cases.
Symptoms of retinitis pigmentosa
In most forms of retinitis pigmentosa, the rods are damaged first, so typically the initial symptoms experienced are gradual loss of night and peripheral vision. There are many variables to this rare disease. While the effect on visual acuity may be minor in some sufferers, in many it progresses until nothing remains but a small area of central vision. Occasionally, it can lead to complete blindness, but this is uncommon.
More rarely, the disease affects the cones first (sometimes called cone-rod dystrophy). In these cases, symptoms start with with color vision problems and a loss of central vision which cannot be corrected by glasses or contacts.
Retinitis pigmentosa can be diagnosed as early as childhood or may not be detected until later in life. A tendency to trip or bump into objects clumsily when light conditions are low is one sign that may be noticed by friends and family.
How is retinitis pigmentosa diagnosed?
An ophthalmoscope examination is frequently used to diagnose retinitis pigmentosa. During this visual exam, the doctor may dilate your pupil with drops so that he or she can see the retina clearly, and looks for anything abnormal, such as clumps of pigment.
A more technologically-advanced way to diagnose retinitis pigmentosa is with an electroretinograph (ERG). During this test, an electrode is placed on each eye to measure the activity of the retina in response to light stimuli.
Other tests that may be utilized are fluorescein angiography, refraction tests, retinal photography, slit lamp examination and tests for color vision, intraocular pressure, pupil reflex response and peripheral vision (visual field).
Treatment for retinitis pigmentosa
Unfortunately there is no treatment or therapy for this condition at present. Scientists have identified many of the the genes responsible for the disease and the family of the sufferer may be advised to seek genetic counseling to fully understand the implications of this condition.
Some eye doctors believe specially formulated vitamin supplements can slightly slow the progression of vision loss for some patients. Occupational therapy can also help sufferers to adjust to their declining vision in the early stages. Better lighting and low vision aids like magnifiers can help at home and at work.
Research is currently underway to develop an artificial retina. There are a number of different companies working on such a device, but the main idea is generally the same: a camera mounted on a pair of eyeglasses transmits data to a microchip implanted in the retina, which then sends the information to the brain via the optic nerve, creating some degree of vision. The patient would not regain normal sight, but this kind of technology may help them see well enough to do certain tasks, like navigate a room or identify objects. Unfortunately, such devices are only in the early experimental stages and are likely a long way off. But the research does offer sufferers and their families some hope for the future.
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