Retinitis Pigmentosa (RP) is an inherited disorder that affects the light-sensitive cells in the eyes, called the photoreceptors. The photoreceptors are made up of rods and cones. The rods are the cells that are most sensitive to dim light and, therefore, are the primary victim of RP. Cones are responsible for color and central fine-detail vision and are affected secondarily. RP can be caused by a number of disorders. Different genes may cause different degrees of vision loss and the onset and severity can vary as well.
Signs and Symptoms
Most patients with RP will experience night vision loss as an initial symptom. They will struggle to see stars and will have trouble driving at night. The rods are responsible for this type of vision and because they are located in the periphery, a patient might eventually experience a loss of side vision altogether (“tunnel vision”). Patients might test 20/20 but they will be considered legally blind because of the degree to which their peripheral vision is compromised. Eventually the central vision might also deteriorate; the signs of central vision loss can be detected by your eye doctor and include retinal pigmentation with the appearance of “bone-spicule” deposits. This will occur when the arteries that carry oxygen to the retina narrow and the optic nerve – containing the cells that carry the signals to the brain – become pale. Other signs can be detected with more specific tests. For instance, the visual field test might show significant contraction and, when less than 20 degrees of the field remains, the patient is considered legally blind. The elctroretinogram (ERG) measures the electrical signal of the retinal cells in response to light; in advanced cases this reaction is suppressed or perhaps absent altogether. In patients with RP, an ERG will show a loss of the “scotpac signal” or the dark-adapted response of the retina. Other tests like Fluorescein Angiography and Optical Coherence Tomography can detect cell loss or “atrophy” found in RP patients, which might not have been spotted in a regular eye exam. Many patients with RP will develop cataracts, so your eye doctor should keep close watch for the symptoms. Other treatable problems, like Cystoid Macular Edema, might also be detected with these advanced tests. Recently, genetic testing for some forms of RP has been made possible; while the tests are currently used for diagnosis, they may ultimately be useful for treatment, as well.
What is the treatment for Retinitis Pigmentosa?
While there is no cure for RP, there are treatments that can help slow vision loss. Dicosahexaenoic Acid (DHA) and the retinal palmitate form of vitamin A have both been shown to slow visional field loss. Diets enriched in Omega 3 fatty acids have also been shown to slow vision loss. Vitamin E, however, – in doses of 400 IU – has been found to accelerate the progression of RP. If started by the age of 30 and, with the appropriate vitamin regimen and diet, a patient can add as many as 20 years of functional vision to their lives. While there are no reported instances of toxicity in healthy adults taking 15,000 IU of vitamin A palmitate daily, people are advised to have a liver function test completed and their vitamin A blood levels measured before they begin the regimen. These tests should be revisited annually, thereafter. Also, because of the potential for birth defects, women who are pregnant or planning to become pregnant are not advised to take vitamin A palmitate in this dosage. Bone density in women may also be an issue.
For patients with CME, anti-inflammatory drops/injections and a diuretic, called Acetazolamide, may be effective. PSC cataract is amenable to surgery. Clinical trials with stem cells and growth factor replacement are currently underway and the specialists at RMI have helped pioneer some of the treatments. We keep our patients up-to-date about the latest trials and treatment options, so to help them maximize their visual potential.