First Incidence and Progression Study for Diabetic Retinopathy in Portugal, the RETINODIAB Study: Evaluation of the Screening Program for Lisbon Region.

Purpose: To estimate the 5-year incidence and progression of diabetic retinopathy (DR) among persons with type 2 diabetes mellitus (DM).

Design: Population-based, prospective, cohort study.

Participants: The RETINODIAB (Study Group for Diabetic Retinopathy Screening) program was implemented in the Lisbon and Tagus Valley area between July 2009 and December 2014. A total of 109 543 readable screening examinations were performed and corresponded to 56 903 patients who attended the screening program at entry. A total of 30 641 patients (53.85%) had at least 1 further screening event within the study period and were included in the analysis.

Methods: Participants underwent two 45° nonstereoscopic retinal digital photographs per eye according to RETINODIAB protocol. All images were graded according to the International Clinical Diabetic Retinopathy Scale. Referable diabetic retinopathy (RDR) was defined for all patients graded as moderate nonproliferative DR (NPDR), severe NPDR, or proliferative DR (PDR), with or without maculopathy or mild NPDR with maculopathy. Nonparametric estimates of the annual and cumulative incidences were obtained by Turnbull's estimator. Associations between the potential risk factors and the time to onset/progression of retinopathy were assessed through a parametric survival analysis for interval-censored data.

Main Outcome Measures: The authors estimated the onset and progression incidence rates of DR.

Results: Yearly incidence of any DR in patients without retinopathy at baseline was 4.60% (95% confidence interval [CI], 3.96-4.76) in the first year, decreasing to 3.87% (95% CI, 2.57-5.78) in the fifth year. In participants with mild NPDR at baseline, the progression rate to RDR in year 1 was 1.18% (95% CI, 0.96-1.33). Incidence of any DR and RDR and DR progression rate were associated with known duration of diabetes, age at diagnosis, and use of insulin treatment.

Conclusions: This longitudinal epidemiologic study provides the first Portuguese incidence DR data in a large-scale population-based cohort of type 2 diabetes after a 5-year follow-up. Duration of diabetes, age at diagnosis, and insulin treatment were associated with increasing risk of incidence and progression of DR. A personalized schedule distribution of screening intervals according to the individual patient's profile should be implemented, with resulting benefits in terms of health costs.