Normal vision. Courtesy NIH National Eye InstituteThe same view with tunnel vision from retinitis pigmentosa
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Retinitis pigmentosa

Retinitis pigmentosa, or RP, is a genetic eye condition. Generally, night blindness 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. more...

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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

Mottling of the retinal pigment epithelium with bone-spicule pigmentation is typically pathognomonic for retinis pigmentosa. Other ocular features include waxy pallor of the optic nerve head, attenuated retinal vessels, cellophane maculopathy, cystic macular edema, and posterior subcapsular cataract.

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 , gene therapy, stem cells, nutritional supplements, and/or drug therapies.

Sources

Jones BW, CB Watt, JM Frederick, W Baehr, CK Chen, EM Levine, AH Milam, MM LaVail, RE Marc 2003 Retinal remodeling triggered by photoreceptor degenerations. J Comp Neurol 464: 1-16.

Marc RE, BW Jones 2003 Retinal remodeling in inherited photoreceptor degenerations. Molecular Neurobiology 28: 139-148.

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Vitamins A and E in the treatment of retinitis pigmentosa
From Nutrition Research Newsletter, 7/1/93

Retinitis pigmentosa is a collective name for a group of hereditary disorders involving degeneration of the retina, with progressive loss of vision, affecting about one in 3000 individuals worldwide. Patients typically develop night blindness in adolescence, followed by a loss of peripheral vision and eventually a loss of central vision in older adulthood. Both vitamin A and vitamin E have been. investigated as possible therapies in retinitis pigmentosa. Uncontrolled observations of patients who were treating themselves with these vitamins have suggested that supplementation might slow the progression of the disease.

This study, from the Massachusetts Eye and Ear Infirmary, Boston, was a randomized, controlled, double-masked trial of vitamin A and vitamin E supplementation in 601 patients with retinitis pigmentosa. The patient, aged 1849 years, were randomly assigned to receive 15,000 IU of vitamin A (as retinyl palmitate), 400 IU of vitamin E, both vitamins, or a placebo (containing trace levels of the vitamins) daily for four to six years. The principal outcome measure was cone electroretinogram amplitude, an objective measure of retinal function.

Patients receiving vitamin A (with or without vitamin E) showed a slower rate of decline in retinal function, as measured by cone electroretinogram amplitude, in comparison with those not receiving vitamin A. Vitamin E showed no effect in the group as a whole. However, in a subgroup of patients with initially better retinal function, those receiving vitamin E showed a faster rate of decline in retinal function than those not receiving the vitamin.

"These results support a beneficial effect of 15,000 IU/ d of vitamin A and suggest an adverse effect of 400 IU/ d of vitamin E on the course of retinitis pigmentosa." The authors recommend that "most adult patients with the common forms of retinitis pigmentosa" should take a vitamin A supplement under medical supervision and that these patients should avoid the use of high-dose vitamin E supplements.

An accompanying editorial offers a different view. Although the editorial writers praise the design, execution, and analysis of the trial, they express caution about the investigators' conclusions and recommendations. Their principal concern is that the apparent beneficial effects involved electroretinogram measures only; there was no significant benefit for any measure of actual visual function. The editorial writers suggest several mechanisms by which vitamin A or vitamin E supplementation might influence cone electroretinogram amplitude without affecting vision. They also point out that there may be adverse effects associated with long-term vitamin A supplementation.

The editorial states, "We believe that the important observations of this study are strictly limited to the electroretinogram measures. Without a better understanding of the reason for the electroretinogram effects, we cannot conclude from the data that supplemental vitamin A alters the natural course of retinitis pigmentosa .... Given the somewhat speculative nature of the possible clinical benefits of vitamin A supplementation for retinitis pigmentosa, the potential risks of this therapy take on greater significance .... Our recommendation is to inform patients of the results of this study and of the potential risks of supplemental vitamin A and to caution them that the results of the study apply only to the electroretinogram and may not be generalizable to the loss of visual function."

Eliot L Berson et al, A Randomized Trial of Vitamin A and Vitamin E Supplementation for Retinitis Pigmentosa, Archives Opthalmology 111(6):761-772 (June 1993) [Reprints: Eliot L Berson, MD, Berman-Gund Laboratory, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston MA 021141

Robert W Massof and Daniel Finkelstein, Supplemental Vitamin A Retards Loss of ERG Amplitude in Retinitis Pigmentosa [Editorial], Archives Opthalmology 111(6): 751- 754 (June 1993)

[Editor's note: This study also provides toxicity data on vitamin A: 15,000 IU taken on a daily basis for four to six years did not have any adverse effects.]

COPYRIGHT 1993 Frost & Sullivan
COPYRIGHT 2004 Gale Group

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