Diabetic retinopathy in Victoria, Australia: the Visual Impairment Project

Abstract

The aim of this study was to establish the prevalence, severity, and risk factors for diabetic retinopathy in a representative sample of Victorian residents aged >= 40 years.A population-based cluster sampling method was used to recruit 4,744 participants (86% participation rate) between 1992 and 1996. Nine suburban Melbourne clusters and four rural Victorian clusters were randomly selected. A private household census was conducted to identify permanent household members aged >= 40 years who were classified as eligible residents. At locally established test sites, participants provided a detailed medical and personal history and underwent an ocular examination including dilated funduscopy and fundus photography. The interview included specific questioning about whether participants had ever been diagnosed with diabetes mellitus and the year in which such a diagnosis was made. Participants with previously diagnosed diabetes were also asked if and when their last dilated fundus examination had been conducted and who performed the examination.

Two 30° fields of the fundus were photographed in each eye; one centered on the optic disk and the other centered on the fovea. Levels of diabetic retinopathy in people with previously diagnosed diabetes were defined, according to the Academy of Ophthalmology in the United States, as mild nonproliferative, moderate nonproliferative, severe nonproliferative, and proliferative diabetic retinopathy. All participants at rural test sites were asked to provide a finger-prick blood sample to measure glycosylated hemoglobin (HbAlc) percentages. Glaucoma status was evaluated by a consensus panel comprised of six ophthalmologists, including two glaucoma specialists. This panel determined glaucoma status on the basis of Humphrey visual fields and photographs of the optic disk. Presenting visual acuity was determined with an Early Treatment Diabetic Retinopathy Study 4-meter chart. Myopia was defined as a best-corrected minus spherical equivalent of > -0.5 D in either eye.