Retinitis pigmentosa
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Retinitis pigmentosa, or RP, is a genetic eye condition. Generally, night blindness precedes tunnel vision by years or even decades. Many people with RP don't become legally blind until their 40s or 50s and retain some sight all their life. Others go completely blind from RP, in some cases as early as childhood. Progression of RP is different in each case.
RP is a group of inherited disorders in which abnormalities of the photoreceptors (rods and cones) or the retinal pigment epithelium (RPE) of the retina lead to progressive visual loss. Affected individuals first experience defective dark adaptation or nyctalopia (night blindness), followed by constriction of the peripheral visual field and, eventually, loss of central vision late in the course of the disease.
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Diagnosis
The diagnosis of RP relies upon documentation of progressive loss in photoreceptor function by electroretinography (ERG) and visual field testing. The mode of inheritance of RP is determined by family history. At least 35 different genes or loci are known to cause nonsyndromic RP. DNA testing is available on a clinical basis for RLBP1 (autosomal recessive, Bothnia type RP), RP1 (autosomal dominant, RP1), RHO (autosomal dominant, RP4), RDS (autosomal dominant, RP7), PRPF8 (autosomal dominant, RP13), PRPF3 (autosomal dominant, RP18), CRB1 (autosomal recessive, RP12), ABCA4 (autosomal recessive, RP19), and RPE65 (autosomal recessive, RP20). For all other genes, molecular genetic testing is available on a research basis only.
RP can be inherited in an autosomal dominant, autosomal recessive, or X-linked manner. X-linked RP can be either recessive, affecting primarily only males, or dominant, affecting both males and females, although females are always more mildly affected. Some digenic and mitochondrial forms have also been described. Genetic counseling depends on an accurate diagnosis, determination of the mode of inheritance in each family, and results of molecular genetic testing. RP combined with progressive deafness is called Usher syndrome.
Treatment
There is currently no medical treatment for retinitis pigmentosa, although scientists continue to investigate possible treatments. Future treatments may involve retinal transplants, artificial retinal implants [1] (http://www.scienceblog.com/cms/node/6906), gene therapy, stem cells, nutritional supplements, and/or drug therapies.
From 2002-2004, six RP patients were fitted with one intraocular retinal prosthesis (more popularly referred to as an artificial retina) in their "worse eye." Follow-up exams showed that the six patients were able to count and describe the position of high contrast objects with 74-99% accuracy. The subjects were also able to discern simple shapes such as the orientation of a bar or the capital letter L with 61-80% accuracy.
External links
- Retinitis Pigmentosa (http://www.nlm.nih.gov/medlineplus/ency/article/001029.htm) (Medline Plus).
- More about Retinitis Pigmentosa (http://merritew.tripod.com/retinitispigmentosa)
Sources
- M.S. Humayun, R. Freda, I. Fine, A. Roy, G. Fujii, R.J. Greenberg, J. Little, B. Mech, J.D. Weiland, E. de Juan, Jr., "Implanted Intraocular Retinal Prosthesis in Six Blind Subjects," ARVO 2005, Retinal Prosthesis Ide:Retinitis Pigmentosa