About one in 4,000 people, or about 2 million worldwide, have retinitis pigmentosa. The condition typically results in night blindness in adolescence before the loss of side vision in young adulthood, followed by tunnel vision as it worsens and virtual blindness by the time a patient turns 60, researchers write in the study background.
Eliot L. Berson, M.D., of the Massachusetts Eye and Ear, and Harvard Medical School, and colleagues analyzed visual acuity data from three clinical trials conducted involving patients with typical retinitis pigmentosa from 1984 to 1991, 1996 to 2001 and 2003 to 2008. A total of 357 patients were included in the current study and all were taking vitamin A palmitate (15,000 IU/d).
Their results indicate that patients with a diet high in long-chain ω-3 fatty acids (≥0.20 g/d) had a 40 percent slower mean (average) annual rate of decline in distance visual acuity than those with a diet low in those fatty acids, the researchers comment.
The researchers further note that they previously reported an effect of dietary ω-3 intake on retaining central visual field sensitivity. Patients receiving vitamin A palmitate, 15,000 IU/d, with ω-3 intake of at least 0.20 g/d had almost a 50 percent slower rate of decline in central visual field sensitivity than those receiving this dose of vitamin A with a lower ω-3 intake.
“Therefore, the treatment regimen of vitamin A combined with an ω-3-rich diet (≥0.20 g/d) should make it possible for many patients with typical retinitis pigmentosa to retain both visual acuity and central visual field for most of their lives,” the researchers conclude.
The authors also comment about the rate of decline in letters per year on Early Treatment Diabetic Retinopathy Study (ETDRS) distance acuity testing. They explain the mean (average) rate of decline in letters per year was 0.59 letter for patients receiving vitamin A with high ω-3 intake vs. 1.00 letter for patients receiving vitamin A with low ω-3 intake over a four to six year period. They estimate what this could mean over the long term.
“A representative patient who starts receiving vitamin A by age 35 years and eats an ω-3-rich diet (i.e. one to two 3-ounce servings of oily fish per week) with an ETDRS acuity of 50 letters (equivalent to 20/30 on the Snellen chart) would, on average, be expected to decline to an ETDRS acuity of 24 letters (equivalent to 20/100 on the Snellen chart) at age 79 years, whereas this patient receiving vitamin A with a low dietary ω-3 intake (e.g. less than one 3-ounce serving of oily fish per week) would decline to this level at age 61 years,” they conclude.
“We are sometimes asked how one or two nutritional supplements can benefit patients with so many different gene defects,” Dr. Berson said. “With respect to vitamin A, we and others have suggested that under daylight conditions rods give cones vitamin A via Müller cells. Interphotoreceptor retinoid binding protein (IRBP) transports vitamin A between these cells. Release of vitamin A from IRBP requires DHA present in oily fish. Rod degeneration leads to a deficiency of vitamin A and DHA. This could explain why vitamin A plus an oily fish diet benefits patients with RP. Patients are advised to take vitamin A to replace their rods and eat oily fish to enhance delivery of vitamin A to cones.”
This study was supported by the National Eye Institute and the Foundation Fighting Blindness, Columbia, Md. Please see the article for additional information, including other authors, financial contributions and affiliations, financial disclosures, funding and support, etc.
(Arch Ophthalmol. doi:10.1001/archopthalmol.2011.2580)
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