Retinitis pigmentosa is an eye disease in which there is damage to the retina. Approximately 2 million individuals (about 1 in 4,000) worldwide are affected by the condition, which typically results in night blindness. Symptoms usually first appear in childhood, but severe vision problems, such as loss of side vision, tunnel vision, and virtual blindness, do not usually develop until early to late adulthood.
Visual acutiy data from 3 human trials conducted from 1984 to 1991, 1996 to 2001 and 2003 to 2008, involving individuals with typical retinitis pigmentosa, were examined by Eliot L. Berson, M.D., of Harvard Medical School and the Massachusetts Eye and Ear Infirmary, Boston, and his team. In the current study, the team enrolled 357 individuals with the condition, who were all taking vitamin A palmitate (15,000 IU/d).
Results from the study revealed that the mean (average) annual rate of decline in distance visual acuity was 40% slower among participants who consumed a diet high in long-chain ω-3 fatty acids (≥0.20 g/d), compared with participants whose diet was low in omega-3 fatty acids.
In a previous study, the team revealed that dietary omega-3 intake had an effect on retaining central visual field sensitivity. They found that individuals receiving ω-3 intake of at least 0.20 g/d, in conjunction with vitamin A palmitate, 15,000 IU/d had nearly a 50% slower rate of decline in central visual field sensitivity than patients receiving a lower omega-3 intake and the same dose of vitamin A.
"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."
Commenting about the rate of decline in letters per year on Early Treatment Diabetic Retinopathy Study (ETDRS) distance acuity testing, the researchers explain that the mean rate of decline in letters per year was 0.59 letter for individuals receiving hight omega-3 intake, combined with vitamin A, compared to 1.00 letter for individuals receiving low omega-3 intake, combined with vitamin A, over a 4 to 6 year period.
The researchers estimate:
"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."