Diabetic retinopathy occurs when excess glucose causes structural changes to blood vessels of the retina at the back of the eye. It is the most common cause of vision loss among older people with Type 1 and Type 2 diabetes, and the leading cause of vision impairment and blindness among working-age adults (1). In the early stages of the condition, there is a narrowing of the retinal arteries associated with reduced retinal blood flow and dysfunction of the neurons of the inner retina. In later stages, changes in the function of the outer retina causes some initial minor loss of visual acuity. As the condition progresses, the base membrane of the retinal blood vessels thickens, capillaries degenerate (leading to loss of blood flow), and microscopic balloon-like structures (aneurysms) jut out from the capillary walls causing advanced dysfunction and degeneration of the neurons and glial cells of the retina (2,3). At this stage, there is considerable loss of vision which can progress to total blindness.
A new “Journal of the American Medical Association” (JAMA) article (4) provides some initial evidence that regular intake of marine omega-3 fatty acids can help delay the onset of diabetic retinopathy in older adults with Type 2 diabetes. The paper makes an observational study of a subset of data from the PREDIMED randomised controlled trial in Spain (5) where the participants were assessed for a series of clinical end points after following various forms of the Mediterranean diet. The use of a detailed validated dietary questionnaire enabled a realistic assessment of the intake of marine omega-3s. The subset cohort consisted of 3,482 older persons with Type 2 diabetes and average age of 67.5 years. At the follow up period of an average of 6 years, 0.17 percent of the group consumed more than 500mg per day of marine omega-3s developed diabetic retinopathy compared with 0.49 percent for the group that consumed less than 500mg per day. The European Commission authorized a health claim for the general healthy population to be used for “maintenance of normal vison” on foodstuffs that contribute to intakes of 250mg per day or more of the omega-3 fatty acid docosahexaenoic acid (DHA) (6).