RETINOPATHY AND DIET

Moderate consumption of long-chain polyunsaturated fatty acids (PUFAs) may protect against diabetic microangiopathy, suggests a study of a Norwegian coastal population of diabetic patients. “In other words, dietary intake of PUFAs may provide low-cost prophylaxis of diabetic retinopathy,†said Knud Erik Alsbirk MD, private practice, Sotra Eye Clinic, Bergen, Norway, at the 12th EURETINA Congress.

He undertook a study to document the prevalence of visual impairment and diabetic retinopathy among diabetic patients in his clinic population based on his impression from over 20 years of practice that the rates were low, and his hypothesis that it might be related to a high PUFA intake from dietary fish. “My ophthalmological practice is located in an island district on the west coast of Norway where there is a long tradition for and good access to high-quality fish intake,†Dr Alsbirk explained.

Further support for his hypothesis derived from the case of a patient with a 12-year history of Type II diabetes who presented with intraretinal microvascular abnormalities (IRMA) that reversed six months after he recommenced taking an omega-3 supplement. The study included 519 randomly selected patients with diabetes, of whom about 10 per cent had Type I disease. Approximately 85 per cent of patients knew their HBA1c level and at least half were taking an antihypertensive, a statin medication, and an omega-3 fatty acid supplement regularly.

Diagnosis of diabetic retinopathy was made from fundus photographs using criteria of Wilkinson et al. and was identified in 47 per cent of Type I diabetics and 22 per cent of those with Type II disease. However, it was rarely sightthreatening and generally received timely treatment with laser, vitrectomy and anti-VEGF medications if needed. Only 11 per cent of Type I diabetics and five per cent of Type II diabetics had diabetic macular oedema; rates of proliferative diabetic retinopathy in the two subgroups were 13 per cent and three per cent, respectively. Visual function remained good overall. BCVA was less than 6/12 in less than two per cent of the Type II diabetics and in none of the patients with Type I disease.

“The few cases of poor BCVA were all in patients with no or simplex grade I diabetic retinopathy and were attributable to other eye morbidities,†Dr Alsbirk reported. Information on fish consumption from dietary history showed an average weekly intake of 3.2 meals by the Type I patients and 4.4 meals for those with Type II diabetes. When intake of omega-3 supplements or cod liver oil was added in, the average number of fish meals/week increased to 6.3 for the Type I patients and 8.0 for the Type II patients.

Dr Alsbirk noted there are mixed results from previously published preclinical studies investigating the influence of PUFA intake on diabetic retinopathy. In 1996, Hammes et al. reported that fish oil administration to diabetic rats accelerated retinopathy. However, a decade later, Connor et al. found a 40 per cent reduction in pathological angiogenesis in mice with experimentally induced retinopathy given omega-3 PUFAs.

To reconcile the conflicting findings, Dr Alsbirk suggested the answer may lie in the amount of PUFA intake. “It seems safe to conclude from our study that a moderate consumption of PUFAs does not accelerate the progression of diabetic microangiopathy in humans. The adverse effect in the rat study may be because the animals received an average omega-3 dose of 500 mg/kg/day, which is 40-50 times greater than the daily recommended dose,†he said. The authors have no financial disclosure.