Low cumulative incidence of proliferative retinopathy in childhood-onset type 1 diabetes: a 24-year follow-up study

Aims/hypothesis We estimated cumulative incidence of proliferative diabetic retinopathy (PDR) and risk factors for developing diabetic retinopathy (DR) in childhood-onset type 1 diabetes. Materials and methods A sample of 294 patients with childhood-onset type 1 diabetes (<15 years) diagnosed in Norway between 1973 and 1982 was examined for retinopathy at baseline between 1989 and 1990 and at follow-up from 2002 to 2003. At follow-up, mean age was 33 years (range: 21–44), mean diabetes duration 24 years (19–30) and total person-time contributed 7,152 person-years. Retinal photographs were taken at baseline and follow-up. Associations between baseline factors and PDR were estimated using Cox regression models. Results Overall, 262 of 294 (89.1%) developed DR from diabetes onset, of whom 31 developed PDR. The 25-year cumulative incidence of PDR was 10.9% (95% CI 7.3–14.5). Among 194 without retinopathy at baseline, 163 (84%) developed DR and nine (5%) progressed to PDR. Among 97 patients with non-proliferative DR at baseline, 19 (20%) progressed to PDR. Significant predictors for developing PDR were retinopathy at baseline (relative risk [RR]=3.71, 95% CI 1.59–8.68), HbA_1c (RR=2.05, 1.44–2.93), and triglycerides (RR=1.55, 1.06–1.95). Conclusions/interpretation Nine out of every ten patients diagnosed with type 1 diabetes developed DR, but only one out of ten developed PDR within their first 25 years of diabetes duration. The cumulative incidence of PDR is lower than previously reported from other countries. Potentially modifiable risk factors predict the development of DR and PDR.