Omega-3-rich diet plus vitamin A improves visual acuity in patient with retinitis pigmentosa
MedWire News: Eating a diet rich in omega (ω)-3 is associated with reduced annual rates of decline in distance and retinal visual acuities in adults with retinitis pigmentosa receiving vitamin A, say US researchers.
They explain that retinitis pigmentosa affects one in 4000 people, or about 2 million people worldwide. Patients typically report night blindness in adolescence and loss of side vision in young adulthood and, as the condition advances, they develop tunnel vision and some become virtually blind by age 60 years.
These findings suggest that a treatment regimen of vitamin A combined with an ω-3-rich diet "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," comment Eliot Berson (Harvard Medical School, Boston, Massachusetts) and colleagues.
The team analyzed visual acuity data from three clinical trials conducted among patients with typical retinitis pigmentosa from 1984-1991, 1996-2001, and 2003-2008.
All 357 patients were receiving 15,000 IU vitamin A per day for 4 to 6 years. At initial screening and annual follow-up visits they completed a food frequency questionnaire and had an ocular examination, including a measure of Early Treatment Diabetic Retinopathy Study (ETDRS) distance acuity at 3.2m. After dilation, Snellen retinal acuity was also assessed.
Rates of visual acuity decline were compared between those with high (≥0.20 g/day) versus low (<0.20 g/day) ω-3 intake.
Berson and co-authors report that mean annual rates of change of distance and retinal acuity were slower among those with high ω-3 intake than those with low intake.
Specifically, distance acuity declined by 0.59 letters per year in the high-ω-3 intake group versus 1.00 letter per year in the low-intake group. Similarly, retinal acuity decreased by 1.5% per year in the high-intake group versus 2.8% per year in the low-intake group.
There was no significant effect of age on rate of visual acuity decline for either distance or retinal acuity, note the authors. Furthermore, each group showed a similar change in posterior subcapsular cataract diameter, suggesting that the effect of ω-3 intake on distance acuity was not due to cataract enlargement in these patients.
The researchers predict that, if the observed rates are sustained over the long term, a patient who starts receiving vitamin A by age 35 years and eats a diet low in ω-3 (ie, less than one 3-oz serving of oily fish per week), with an ETDRS acuity of 50 letters would, on average, be expected to decline to an ETDRS acuity of 24 letters at age 61 years.
If this patient ate an ω-3-rich diet, however, they would not decline to this level until 79 years of age, concludes the team in the Archives of Ophthalmology.
By Nikki Withers