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Definition
Retinitis pigmentosa (RP) is a group of inherited eye diseases that often leads to severe visual problems. The retina is a layer of light-sensitive tissue that lines the back of the eye. It converts visual images that we see into nerve impulses that it sends to the brain. Some types of RP are associated with other inherited conditions. This disorder is named for the irregular clumps of black pigment that usually occur in the retina with this disease.
Normal Anatomy of the Eye
2008 Nucleus Medical Art, Inc.
Causes
Many types of RP are caused by a genetic mutation. Some cases occur sporadically. Vision loss occurs when light-sensitive cells in the retina gradually break down. There are two types of cells in the retina:
- ConesThese cells are found mostly in the center of the retina. Cones are needed for central vision and to see colors.
- RodsLocated mostly away from the center, rods respond to dim light. They provide night and peripheral vision.
In most forms of retinitis pigmentosa, the rods die. Vision, thus, becomes impaired at night. The ability to see things off to the side while looking ahead also decreases. In some forms of RP, the cones are lost. In those cases, central and color vision suffers. Vision loss usually progresses over a period of many years.
Risk FactorsA risk factor is something that increases your chance of getting a disease or condition. Risk factors for RP include: Family members with RPSex: male Having certain other inherited conditions, including: Fanconis syndromeFriedreichs ataxiaOlivopontocerebellar degenerationBassen-Kornzweig diseaseKearns-Sayre syndromeRefsums disease Symptoms Loss of vision is usually first noted in childhood or early adulthood. The disease gradually worsens. After a number of years, vision loss may become severe. Symptoms vary, depending on the type of retinal cell that is affected. Both eyes often experience similar vision loss. It should be noted that RP is a slowly progressive disease over many years and that most patients never become completely blind. In fact, even though many people with RP are considered legally blind, it is only because they have very constricted fields of vision (poor peripheral vision). Some still maintain excellent central visual acuity. Overall, symptoms may include: Night blindness (the most common symptom)Eyes take longer to adjust to dim lightingTrouble seeing in foggy or rainy weatherEyes are slow to make adjustment from bright sun to indoor lightingDecreased peripheral vision/visual field narrows, often called "tunnel vision"Difficulty seeing colors, especially blueVisual loss, partial or complete, usually gradually progressiveClumsiness from lack of sight, especially in narrow spaces such as doorways Blurry vision from cataracts may complicate RP later in the disease.
DiagnosisYour doctor will ask about your symptoms and medical history, and perform an eye exam. You may be referred to an eye specialist, such as an ophthalmologist. Vision tests may include: Visual field testingto check peripheral vision, which is how well you see off to your side, rather than directly ahead, without moving your eyesVisual acuitychecks how well you can see progressively smaller objects, usually a row of letters or numbersDark adaptometrytests how your vision adapts to darknessColor testingdetermines how well you can differentiate colorsElectroretinogram (ERG)a test to measure electrical activity in the eye. This test identifies the loss of cell function in the retina and is used to track progression of the disease. TreatmentThere is no effective treatment or cure for retinitis pigmentosa. Treatment aims to help you function with the vision that you have. Your doctor can counsel you about expected patterns of vision loss based on the type of RP you have. Recommendations include: Vitamin AOne study implied that large doses of vitamin A can slow the progression of RP by approximately 2% per year. However, the use of this finding is controversial. For one, it is a very mild effect given the large dose. Secondly, there may be side effects of such large doses of vitamin A. Always talk to your doctor before taking any supplements.
Light AvoidanceAlthough no direct link has been established, it is generally recommended that everybody, especially patients with disorders such as RP, wear dark UV-protected sunglasses and a wide-brimmed hat in bright, sunny conditions, such as while skiing or at the beach. Low-vision Aids These may include the following: Magnifying glassesElectronic magnifiers, which project an enlarged image onto a screenNight vision scopes, which enlarge distant objects under conditions of low lightLenses for distant vision (eyeglasses or contacts)Some community organizations offer classes to help people with vision loss adjust and learn how to use vision aids. If you are considered legally blind, you are entitled to many low-vision services at no cost. PreventionOnce RP has been inherited there are no known ways to prevent the disorder from occurring. If you have RP or have a family history of the disorder, you can talk to a genetic counselor when deciding to have children. RESOURCES: The Foundation Fighting Blindnesshttp://www.blindness.org Prevent Blindness Americahttp://www.preventblindness.org RP Internationalhttp://www.rpinternational.org CANADIAN RESOURCES: Canadian Association of Optometristshttp://www.opto.ca/en/public/
The Canadian National Institute for the Blindhttp://www.cnib.ca/en/Default.aspx References: Cecil Textbook of Medicine . 21st ed. WB Saunders Co; 2000. The Foundation of the American Academy of Ophthalmology. Retina and Vitreous, Basic and Clinical Science Course . 2001-2002. Harrison's Principles of Internal Medicine . 14th ed. The McGraw-Hill Companies; 2000. Ophthalmology . Mosby International Ltd; 1999. Last reviewed October 2007 by Marc Ellman, MDPlease be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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