Aims/hypothesis: Most guidelines recommend annual screening for diabetic retinopathy (DR) but limited resources and the slow progression of DR suggest that longer recall intervals should be considered if patients have no detectable lesions. This study aimed to identify the cumulative incidence and time of development of referable DR in patients with no DR at baseline, classified by clinical characteristics.
Methods: Analysis was performed of data collected prospectively over 20 years in a screening clinic based in a teaching hospital according to a consensus protocol. The cumulative incidence, time of development and relative risk of developing referable retinopathy over 6 years following a negative screening for DR were calculated in 4,320 patients, stratified according to age at onset of diabetes (<30 or ≥ 30 years), being on insulin treatment at the time of screening and known duration of diabetes (<10 or ≥ 10 years).
Results: The 6 year cumulative incidence of referable retinopathy was 10.5% (95% CI 9.4, 11.8). Retinopathy progressed within 3 years to referable severity in 6.9% (95% CI 4.3, 11.0) of patients with age at onset ≥ 30 years, who were on insulin treatment and had a known disease duration of 10 years or longer. The other patients, especially those with age at onset <30 years, on insulin and <10 years duration, progressed more slowly.
Conclusions/interpretation: Screening can be repeated safely at 2 year intervals in any patient without retinopathy. Longer intervals may be practicable, provided all efforts are made to ensure adherence to standards in procedures and to trace and recall non-attenders.