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Image:Human eyesight two children and ball normal vision.jpg Normal vision. Courtesy NIH National Eye Institute Image:Human eyesight two children and ball with retinitis pigmentosa or tunnel vision.png The same view with tunnel vision from retinitis pigmentosa Retinitis pigmentosa, or RP, is a group of genetic eye conditions. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not 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.
Signs
DiagnosisThe 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. GeneticsIn 1989, a mutation of Rhodopsin, a gene that plays an essential part in the visual transduction cascade, was identified. Since then, more than 100 mutations have been found in this gene, accounting for 15% of all types of retinal degeneration. Most of those mutations are missense mutation and inherited mostly in a dominant manner. Treatment
In a study published in the journal Nature, researchers working with mice at the University College London Institutes of Ophthalmology and Child Health and Moorfields Eye Hospital, transplanted mouse stem cells which were at an advanced stage of development, and already programmed to develop into photoreceptors, into mice that had been genetically induced to mimic the human conditions of retinitis pigmentosa and age-related macular degeneration. These photoreceptors developed and made the necessary neural connections to the animal's retinal nerve cells, a key step in the restoration of sight. Previously it was believed that that the mature retina has no regenerative ability. This research may in the future lead to using transplants in humans to relieve blindness.[2] See also
BibliographyJones BW, CB Watt, JM Frederick, W Baehr, CK Chen, EM Levine, AH Milam, MM LaVail, RE Marc 2003 Retinal remodeling triggered by photoreceptor degenerations. The Journal of Comparative Neurology 464: 1-16. Marc RE, BW Jones 2003 Retinal remodeling in inherited photoreceptor degenerations. Molecular Neurobiology 28: 139-148. Marc RE, BW Jones, CB Watt and E Strettoi 2003 Review: Neural Remodeling in Retinal Degeneration. Progress in Retinal and Eye Research 22: 607-655. Jones BW and RE Marc. 2005 Review: Retinal remodeling during retinal degeneration. Experimental Eye Research, 81: 121-244 Marc RE, BW Jones and CB Watt. 2005 Review: Retinal remodeling: Circuitry revisions triggered by photoreceptor degeneration. In Plasticity in the Visual system: from Genes to Circuits. Springer, pp. 33-54. Jones BW, CB Watt and RE Marc. 2005 Review: Retinal remodeling in retinal degenerations. Clinical and Experimental Optometry, 88: 282-291.
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