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Retinitis pigmentosa (RP) refers to a group of inherited disorders that slowly lead to blindness due to abnormalities of the photoreceptors (primarily the rods) in the retina.
The retina lines the interior surface of the back of the eye. The retina is made up of several layers. One layer contains two types of photoreceptor cells referred to as the rods and cones. The cones are responsible for sharp, central vision and color vision and are primarily located in a small area of the retina called the fovea. The area surrounding the fovea contains the rods, which are necessary for peripheral vision and night vision (scotopic vision). The number of rods increases in the periphery. The rod and cone photoreceptors convert light into electrical impulses and send the message to the brain via the optic nerve. Another layer of the retina is called the retinal pigmented epithelium (RPE).
In RP, the photoreceptors (primarily the rods) begin to deteriorate and lose their ability to function. Because the rods are primarily affected, it becomes harder to see in dim light, thus causing a loss of night vision. As the condition worsens, peripheral vision disappears, which results in tunnel vision. The ability to see color is eventually lost. In the late stages of the disease, there is only a small area of central vision remaining. Ultimately, this too is lost.
There are many forms of retinitis pigmentosa. Sometimes the disorder is classified by the age of onset or the inheritance pattern. RP can also accompany other conditions. This entry discusses "nonsyndromic" RP, the type that is not associated with other organ or tissue dysfunction.
Approximately 100,000 Americans have RP. It is estimated to affect about one in every 4,000 Americans and Europeans. For other parts of the world, there are no published data. Nor is there any known ethnic difference in the occurrence of RP.
Causes and symptoms
Retinitis pigmentosa is an inherited disease that has many different modes of inheritance. It is known to be caused by more than 100 different genetic mutations. RP, with any inheritance pattern, may be either familial (multiple family members affected) or isolated (only one affected person). In the non-sex-linked, or autosomal, form, it can either be a dominant or recessive trait. In the sex-linked form, called x-linked recessive, it is a recessive trait. This x-linked form is more severe than the autosomal forms. Two rare forms of RP are the digenic and mitochondrial forms.
Isolated RP cases represent 10-40% of all cases. Some of these cases may be the result of new gene mutations (changes in the genes). Other isolated cases are those in which the person has a relative with a mutation in the gene, but the relative is not affected by the condition.
Autosomal dominant RP (AdRP) occurs in about 15-25% of affected individuals. At least 12 different genes have been identified as causing AdRP. People with AdRP will usually have an affected parent. The risk for affected siblings or children is 50%.
Autosomal recessive RP (ArRP) occurs in about 5-20% of affected individuals. More than 16 genes have been identified that cause this type of RP. In ArRP, each parent of the affected person is a carrier of an abnormal gene that causes RP. Neither of these carrier parents is affected. There is a two-thirds chance that an unaffected sibling is a carrier of RP. All of the children of an affected person would be a carrier of the ArRP gene.
Five to 15% of individuals with RP have x-linked recessive RP (XLRP). Six different genes have been identified as the cause of this type of RP. Usually in this type of inheritance, males are affected carriers, while females are unaffected carriers or have a milder form of the disease. The mother may be a carrier of the mutation on the X-chromosome. It is also possible that a new mutation can occur for the first time in an affected person. For families with one affected male, there is a mathematical formula called the Baysean analysis that can be applied to the family history. It takes into account the number of unaffected males to determine whether a female is likely to be a carrier or not. If a mother is a carrier, her children have a 50% chance of inheriting the RP gene. For affected males, all of their daughters will be carriers but none of their sons will be affected.
The digenic form of RP occurs when the affected person has inherited one copy of an altered ROM1 gene from one parent and one copy of an altered peripherin/RDS gene from the other parent. The parents are asymptomatic. Mitochondrial inheritance occurs when the gene mutation is in a mitochondrial gene. People with this type of RP have progressive hearing loss and mild myopathy. Both of these types of RP are very rare.
The first symptoms, a loss of night vision followed by a loss of peripheral vision, usually begin in early adolescence or young adulthood. Occasionally, the loss of the ability to see color occurs before the loss of peripheral vision. Another possible symptom is seeing twinkling lights or small flashes of lights.
When a person complains of a loss of night vision, a doctor will examine the interior of the eye with an ophthalmoscope to determine if there are changes in the retina. For people with advanced RP, the condition is characterized by the presence of clumps of black pigment in the inner retina (intraretinal). However, the appearance of the retina is not enough for an RP diagnosis since there are other disorders that may give the retina a similar appearance. There are also other reasons someone may have night blindness. Consequently, certain electrodiagnostic tests must be performed. An electroretinogram (ERG) determines the functional status of the photoreceptors by exposing the retina to light. The ERG uses a contact lens in the eye, and the output is measured on a special instrument called an oscilloscope. The functional assessments of visual fields, visual acuity, or color vision may also be performed.
The diagnosis of RP can be established when the following criteria are met:
- rod dysfunction measured by dark adaptation test or ERG,
- progressive loss in photoreceptor function,
- loss of peripheral (side) vision,
- both eyes affected (bilaterality).
Molecular genetic testing is available on a research basis. Prenatal diagnosis for this condition has not yet been achieved.
There are no medications or surgery to treat RP. However, researchers continue to seek possible treatments. In 2004, scientists injected stem cells to the back of mouse eyes and stopped retinal degeneration. Scientists are also exploring the possibility of retinal transplantation. Some doctors believe vitamins A and E will slightly slow the progression of the disease in some people. However, large doses of certain vitamins may be toxic and affected individuals should speak to their doctors before taking supplements.
If a person with RP must be exposed to bright sunlight, some doctors recommend wearing dark sunglasses to reduce the effect on the retina. Affected people should talk to their eye doctors about the correct lenses to wear outdoors.
Ophthalmoscope — An instrument, with special lighting, designed to view structures in the back of the eye.
Because there is no cure for RP, the affected person should be monitored for visual function and counseled about low-vision aids (for example, field-expansion devices). Genetic counseling is also appropriate. A three-generation family history with attention to other relatives with possible RP can help to clarify the inheritance pattern. For some people however, the inheritance pattern cannot be discerned.
There is no known cure for RP, which will eventually lead to blindness. The more severe forms will lead to blindness sooner than milder forms.
"Grant Boosts RP Research Into Transplantation." Ophthalmology TImes August 1, 2004: 6.
"Stem Cells Delivered Into Back of Eye Hold Promise for People With Retinitis Pigmentosa, Other Retinal Degenerations; Potential Treatment for Untreatable Blindness Shows Promise in Mice." Ascribe Health News Service September 15, 2004.
American Academy of Ophthalmology. PO Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. http://www.eyenet.org.
American Association of the Deaf-Blind. 814 Thayer Ave., Suite 302, Silver Spring, MD 20910. (301) 588-6545.
American Optometric Association. 243 North Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. http://www.aoanet.org.
Foundation Fighting Blindness. Executive Plaza 1, Suite 800, 11350 McCormick Rd., Hunt Valley, MD 21031. (888) 394-3937. http://www.blindness.org.
National Retinitis Pigmentosa Foundation. 11350 McCormick Rd., Executive Plaza 1, Suite 800, Hung Valley, MD 21031-1014. (800) 683-5555. http://www.blindness.org.
Prevent Blindness America. 500 East Remington Rd., Schaumburg, IL 60173. (800) 331-2020. http://www.prevent-blindness.org.
Genetic Alliance. http://www.geneticalliance.org.
National Federation of the Blind. http://www.nfb.org.
"OMIM—Online Mendelian Inheritance in Man." National Center for Biotechnology Information. http://www.ncbi.nlm.nih.gov/Omim/searchomim.html.
Retinitis Pigmentosa International. http://www.rpinternational.org.
inflammation of the retina.
retinitis circina´ta (circinate retinitis) circinate retinopathy.
cytomegalovirus retinitis opportunistic infection of the retina by cytomegalovirus, seen in immunocompromised patients; symptoms include retinal necrosis and hemorrhage, leading to blindness.
exudative retinitis exudative retinopathy.
retinitis pigmento´sa a group of diseases, frequently hereditary, marked by progressive loss of retinal response (as recorded by the electroretinograph), retinal atrophy, attenuation of retinal vessels, and clumping of the pigment, with contraction of the field of vision. It may be transmitted as a dominant, recessive, or X-linked trait and is sometimes associated with other genetic defects. It may become manifest at the age of two or three years, or it may follow a slow course over a period of years. There is no successful treatment or cure for the condition. Early diagnosis allows the patient to prepare for the eventual loss of vision.
retinitis proli´ferans a condition that may result from intraocular hemorrhage, with neovascularization and the formation of fibrous bands extending into the vitreous from the retina; retinal detachment may result.
suppurative retinitis retinitis due to pyemic infection.
ret·i·ni·tis pig·men·to·'sa (RP),[MIM*268000]
a progressive retinal degeneration characterized by bilateral nyctalopia, constricted visual fields, electroretinogram abnormalities, and pigmentary infiltration of the inner retinal layers; may be sporadic or demonstrate autosomal dominant [MIM*180100], autosomal recessive, or X-linked inheritance [MIM*268000, *312600, *312610].
Synonym(s): pigmentary retinopathy
retinitis pigmentosa(pĭg′mĕn-tō′sə, -mən-)
A hereditary degenerative disease of the retina, characterized by night blindness, pigmentary changes within the retina, and eventual loss of vision.
retinitis pigmentosaNight-blindness disease Ophthalmology A heterogenous group of AR, less commonly, AD, and X-linked forms of retinal degeneration; RP affects 1:3500, and is characterized by nyctalopia and progressive centripetal loss of visual fields progressing to blindness by middle age
ret·i·ni·tis pig·men·to·sa(ret'i-nī'tis pig'men-tō'să)
A hereditary progressive abiotrophy of the neuroepithelium, with atrophy and pigmentary infiltration of the inner layers of the retina.
retinitis pigmentosaA slow degenerative disorder of the rods and cones of the RETINAS of both eyes with migration of pigment from the retinal pigment layer. Initially, this causes night blindness only but later there is progressive loss of an ever-enlarging area of the peripheral field of vision. This condition is not inflammatory and the term is misnomer. Retinitis pigmentosa varies greatly in age of onset and severity. In 60 percent of cases it has a known genetic basis and more than 45 causal genes have been identified. The remainder are also believed to be caused by gene mutations. A small proportion of cases are due to a gene mutation that prevents retinaldehyde from being converted to the form used by retinal photoreceptors. Some recessive forms are caused by mutations in ABCA4 GENES. There is no specific treatment but nutritional supplements including omega-3-rich fish oils are believed to slow progress. Also known as tapetoretinal degeneration or pigmentary retinopathy.
retinitis pigmentosa (RP)
A primary pigmentary dystrophy of the retina followed by migration of pigment. It is in most cases an inherited disease caused by abnormalities of many genes and characterized by night blindness (nyctalopia) and constricted visual fields. The inheritance can be autosomal dominant, autosomal recessive or X-linked. Many cases are caused by mutations in the rhodopsin gene (RHO). The condition is usually bilaterally symmetrical. The rod system is damaged but cones are also involved to some degree and the electroretinogram amplitude is subnormal. The disease usually begins in adolescence with night blindness, followed by a ring scotoma in the periphery that spreads until only a small contracted central field remains and vision is greatly reduced or completely lost. Ophthalmoscopic examination reveals a yellowish atrophy of the optic nerve, severe arterial attenuation and conspicuous pigment proliferation, which begins in the equatorial region. The areas of pigment have dense centres and irregular processes shaped like bone corpuscles. There are several variants (atypical RP) of pigment distributions and patterns throughout the fundus (e.g. in mainly one quadrant) or as retinitis punctata albescens (scattered white dots most numerous at the equator). Associated systemic syndromes include Bassen-Kornzweig, Kearns-Sayre, Laurence-Moon-Bardet-Biedl, Refsum's and Usher's. Syn. primary pigmentary retinal dystrophy. See visual field field; leopard fundus; tritanopia; tunnel vision.