Retinitis Pigmentosa (RHO, PRPH2/RDS, USH2A, RPGR, ABCA4)
Nonsyndromic Retinitis Pigmentosa (RP, OMIM # 268000) is a large group of inherited degenerative diseases of the retina characterized by abnormalities of the photoreceptors or the retinal pigment epithelium (RPE). It is a progressive disease. Symptoms usually begin with night blindness, progressing to constriction of the peripheral visual field and, eventually, to loss of central vision. The age of onset varies from childhood to middle age (Gu et al. J Med Genet 36:705-707, 1999). The clinical hallmarks are abnormal fundus with bone-spicule deposits and attenuated retinal vessels, abnormal electroretinographic findings and reduced visual fields (Daiger et al. Arch Ophthalmol 125:151-158, 2007). RP affects ~1 in 3,000 people worldwide (Farrar et al. EMBO J 21:857-864, 2002). Genetic abnormalities are the primary cause of RP.
To slow the disease progression, early implementation of vitamin A palmitate, docosahexaenoic acid (DHA), along with the avoidance of vitamin E and excessive sunlight exposure is recommended. Oral acetazolamide or topical dorzolamide are shown to be potential therapies for the benefit of visual acuity and to reduce cystic macular lesions in RP patients (Fahim et al., GeneReviews. 2013; ncbi.nlm.nih.gov/books/NBK1417).
Vitamin A and DHA Therapies
Studies done on patients with RP treated with DHA after previous supplementation with vitamin A found that the duration of vitamin A supplementation is inversely related to the decline of electroretinogram (ERG) amplitude (Berson et al., JAMA Opthalmology. 2004; 122(9): 1306-1314). Patients receiving vitamin A treatment were 32% less likely to decline in visual amplitude than those receiving no treatment (Rosner et al., Archives of Opthalmology. 1993; 111(6): 761-772). In contrast, Vitamin A supplementation and excessive sunlight exposure should be avoided in RP patients with ABCA4 mutations to avoid the accumulation of toxic lipofuscin in the RPE, which emphasizes the importance of genetic testing (Radu et al., Invest Ophthalmol Vis Sci. 2008; 49(9):3821-9).
Oral Acetazolamide Therapy
A follow-up study on long-term effect of acetazolamide treatment suggested that the effect was better in patients with quiescence of uveitis than in those with chronic uveitis. However, the treatment effect is limited by persisting inflammation (Schilling et al., Retina. 2005; 25(2):182-8).
Topical Dorzolamide Therapy
Recent studies have shown that topical dorzolamide chlorhydrate can replace oral acetazolamide therapy by having the same treatment effects, but through eye drops for patients who cannot tolerate systemic effects of oral ingestion (Pacella et al., Ophthalmology and Eye Diseases. 2014; 6: 21-26).
This article is a summary of information that has been reported in the biomedical research literature. It is not medical advice for patients. All disease treatments should be under the direction of a qualified healthcare provider.