Background: Incidence data on which to base targets and protocols for screening for sight-threatening diabetic retinopathy are few. We aimed to investigate yearly and cumulative incidence of any retinopathy, maculopathy, and sight-threatening diabetic retinopathy in patients with type 2 diabetes in an established systematic programme and to calculate optimum screening intervals according to retinopathy grade at baseline.
Methods: We investigated all patients with type 2 diabetes registered with enrolled general practices (except those who were attending an ophthalmologist) who had retinopathy data available at baseline and at least one further screening event. To screen patients, we used non-stereoscopic three-field mydriatic photography and modified Wisconsin grading. Sight-threatening diabetic retinopathy was defined as moderate preproliferative retinopathy or worse, or clinically significant maculopathy in either or both eyes.
Findings: Results were obtained from 20 570 screening events. Yearly incidence of sight-threatening diabetic retinopathy in patients without retinopathy at baseline was 0.3% (95% CI 0.1-0.5) in the first year, rising to 1.8% (1.2-2.5) in the fifth year; cumulative incidence at 5 years was 3.9% (2.8-5.0). Rates of progression to sight-threatening diabetic retinopathy in year 1 by baseline status were: background 5.0% (3.5-6.5), and mild preproliferative 15% (10.2-19.8). For a 95% probability of remaining free of sight-threatening diabetic retinopathy, mean screening intervals by baseline status were: no retinopathy 5.4 years (95% CI 4.7-6.3), background 1.0 years (0.7-1.3), and mild preproliferative 0.3 years (0.2-0.5).
Interpretation: A 3-year screening interval could be safely adopted for patients with no retinopathy, but yearly or more frequent screening is needed for patients with higher grades of retinopathy.