Incidence of sight-threatening retinopathy in Type 1 diabetes in a systematic screening programme

To measure the cumulative incidence of any retinopathy, maculopathy and sight-threatening diabetic retinopathy (STDR), and calculate optimal screening intervals by retinopathy grade at baseline for patients with Type 1 diabetes attending an established systematic retinal screening programme.

All patients with Type 1 diabetes registered with enrolled general practitioners, excluding only those attending an ophthalmologist, were studied if retinopathy data was available at baseline and at least one further screen event. Screening utilized non-stereoscopic 3-field mydriatic photography and modified Wisconsin grading. STDR was defined as moderate pre-proliferative retinopathy or greater and/or significant maculopathy in any eye.

Patients (n=501) underwent 2742 screen events. Cumulative incidence of STDR in patients without baseline retinopathy was 0.3% (95% CI 0.0-0.9) at 1 year, rising to 3.9% (1.4-5.4) at 5 years. Rates of progression to STDR in patients with background and mild pre-proliferative retinopathy at 1 year were 3.6% (0.5-6.6) and 13.5% (4.2-22.7), respectively. Progression to STDR was greater in patients with a higher grade of baseline retinopathy (P=0.001) or a longer disease duration (P=0.003). For a 95% likelihood of remaining free of STDR, mean screening intervals by baseline status were: no retinopathy 5.7 (95% CI 3.5-7.6) years, background 1.3 (0.4-2.0) years and mild pre-proliferative 0.4 (0-0.8) years.

Screening at 2-3 year intervals, rather than annually, for patients without retinopathy in Type 1 diabetes is feasible because of the low risk of progression to STDR, and may result in significant cost savings for a screening programme. Patients with higher grades of retinopathy require screening at least annually or more frequent.