Retinitis pigmentosa also referred to as RP is a genetic eye condition in which the vision progresses from night blindness to tunnel vision. The progression can take place over years, even decades. Many individuals become legally blind in their 40s or 50s. Some individuals with RP can keep some sight their entire life. Others will go completely blind as early as childhood. Progression from night blindness to tunnel vision to complete blindness varies from patient to patien.
RP is an inherited disorder. Progressive visual loss is due to atypical photoreceptors, also known as rods and cones in the retinal pigment epithelium. Retinal pigment epithelium (RPE) is the pigment cell sheet that feeds the retinal cells. The RPE is attached to an intricate system of blood vessels. Individuals first experience night blindness, then a constriction of the peripheral vision field (tunnel vision) and eventually the center vision, which is complete blindness.
When looking into the eye, an ophthalmologist can see a speckling of the retinal pigment epithelium with bone-spicule pitmentation. This is the typical pathology indicator of retinitis pigmentosa. Other features are a waxy sheen of the optic nerve head, long tapering retinal vessels, cellophane maculopathy, posterior subcapsular cataract and cystic macular edema (swelling).
Diagnosis is based upon a records of progressive loss in two test: the photoreceptor function by electroretinography (ERG) and visual field testing. Currently, over thirty-five genes are known to cause non-syndromic RP. DNA testing is available for about nine of the genes that are identified with RP. Testing for other genes that are associated with inherited RP are performed only in research trials.
RP can be inherited in a variety of ways. Autosomal dominant, autosomal recessive, and x-linked manner RP are the inheritance factors. X-linked RP can either be dominant or recessive, that it it can affect men or men and women. Some digenic and mitochondrial forms of RP have also been documented. Genetic counseling is based on an accurate diagnosis, determining the mode of inheritance in the family of the father and mother of the individual and usually leads to further molecular genetic testing. Usher Syndrome is a combination of RP and progressive deafness.
The genetic discover of a mutation of Rhodopsin was made in 1989. This gene has an essential role in the vision transduction cascade. Since 1989 over 100 mutations of this gene have been identified, responsible for 15% of all categories of retinal degeneration. Most of the mutations are referred to as missense mutations and are dominant inherited.
Unfortunately there currently is no cure for retinitis pigmentosa.
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