Prevalence and 25 year incidence of proliferative retinopathy among Danish type 1 diabetic patients

Aims/hypothesis This study aimed to evaluate the prevalence of retinopathy in long-surviving type 1 diabetic patients. It also investigated the 25 year incidence of proliferative retinopathy and associated risk factors in a Danish population-based cohort. Methods A population-based cohort of 727 type 1 diabetic patients from Fyn County, Denmark, was identified in 1973. In 1981-1982, baseline retinopathy was graded and other risk factors were assessed in 573 patients. Twenty-five years later, 308 patients were still alive. Of these, 201 (65.3%) were re-examined at follow-up in 2007-2008. Results The median age and duration of diabetes at follow-up were 58.8 and 43 years, respectively. At follow-up, the prevalence of diabetic retinopathy was 97.0%. Non-proliferative retinopathy was found in 45.8%, and 51.2% had proliferative retinopathy. The 25 year incidence of proliferative retinopathy was 42.9% among patients at risk. In a multivariate analysis, baseline HbA₁ (OR 2.14 per 1% increase, 95% CI 1.06-4.31) and non-proliferative retinopathy (OR 4.61, 95% CI 1.94-11.0) were the only risk factors for incident proliferative retinopathy. The long-term incidence of proliferative retinopathy was not associated with baseline duration of diabetes, proteinuria, smoking, body mass index, maculopathy or systolic or diastolic blood pressure. Conclusions/interpretation Retinopathy among long-surviving type 1 diabetic patients is almost universal. Proliferative retinopathy was found in half of these patients. In addition, the 25 year incidence of proliferative retinopathy was high. Baseline glycaemic regulation and non-proliferative retinopathy were identified as risk factors for incident proliferative retinopathy.