Barbara Boughton

November 05, 2009

November 5, 2009 (San Francisco, California) — Myopia might have a protective effect against diabetic retinopathy, especially sight-threatening diabetic retinopathy, according to research presented here at the American Academy of Ophthalmology Joint Annual Meeting With the Pan-American Association of Ophthalmology.

Myopia that results from longer axial length and greater depth of the front eye chamber might be particularly protective against diabetic retinopathy and result in reduced risk for the eye disease, according to a study authored by Shen Lim, MRCS, and colleagues from the Singapore National Eye Centre.

"The idea that myopia is associated with a reduced risk of diabetic retinopathy has been a common clinical impression for many years," said Dr. Lim. Although earlier smaller studies suggested a protective effect, their results were inconclusive. Dr. Lim's study is the first to include axial length in its analysis of the relation between diabetic retinopathy and myopia. Until now, it's been unclear whether the associations reported in previous studies were related to conditions such as cataract or axial myopia, he said. About 10% of people with diabetes develop diabetic retinopathy.

In the study, subjects were selected from the Singapore Malay Eye Study, a population-based cross-sectional study of urban Malay adults living in Singapore. Of 3280 participants, 675 (20.6%) were found to have diabetic retinopathy. Diabetes mellitus was identified from plasma glucose levels, physician diagnoses, or self-reported use of diabetic medications. Diabetic retinopathy was graded from retinal photographs, and anterior chamber depth and axial length were measured with partial coherence laser interferometry.

Results indicated that participants whose eyes were more myopic, with deeper anterior chamber and longer axial length, were less likely to have diabetic retinopathy; the association was particularly significant for sight-threatening diabetic retinopathy. Although the protective effect of myopia was continuous, even those with mild myopia had a significantly decreased risk for diabetic retinopathy. This protective effect is consistent with most other studies completed to date, Dr. Lim explained, and strengthens ideas about the intimate relationship between cataract, diabetes, and refractive changes, he said.

Dr. Lim and colleagues suggested several hypotheses for the protective effect of myopia on the risk for diabetic retinopathy. Myopic eyes might sustain atrophy of the retina, choroid or vitreous, reducing metabolic needs and improving oxygen circulation in the back of the eye. "As the eye is stretched and the retina becomes thinner, the amount of blood flow is reduced," Dr. Lim said.

Although the study is interesting, its conclusions are not entirely unexpected, said Abdhish R. Bhavsar, MD, director of clinical research at the Retina Center of Minnesota and attending surgeon at the Phillips Eye Institute in Minneapolis. "Myopic eyes are anatomically and structurally different and it is possible that the difference in choroidal or retinal blood flow contributes to the reduced risk of retinal and choroidal vascular diseases," he said.

Dr. Lim has disclosed no relevant financial relationships. Dr. Bhavsar reports receiving current research funds, past honoraria, travel expenses, and/or serving on the advisory boards of Allergen, DRCR, Genentech, Ista, Novartis, and Pfizer.

American Academy of Ophthalmology Joint Annual Meeting With the Pan-American Association of Ophthalmology (AAO-PAAO): Abstract PO265. Presented October 25, 2009.

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