Hyperglycemia, blood pressure, and the 9-year incidence of diabetic retinopathy: The Barbados Eye Studies

Objectives: To evaluate factors related to the incidence of diabetic retinopathy (DR) in a population of African descent, after 9 years of follow-up. Design: Population-based cohort study; 81% participation after 9 years. Participants: Three hundred twenty-four participants of the Barbados Eye Studies, with diabetes mellitus (DM) at baseline and at risk for developing DR during follow-up. Methods: Diabetes-related changes were assessed by masked gradings of baseline and follow-up photographs using a standardized system. The 9-year cumulative incidence of DR was based on participants with DM and free of retinopathy at baseline; incidence rates were estimated by the product-limit approach. Cox regression models for discrete-time data were used to evaluate risk factors associated with the 9-year incidence of DR. Results: Multivariate analyses revealed that older age at DM onset decreased the 9-year risk of DR development; for each 10 years of older age at onset, the risk of DR decreased by 30% (risk ratio [RR], 0.7; 95% confidence interval [CI], 0.56-0.96). The risk of DR doubled among persons with DM duration between 5 and 9 years (RR, 2.1; 95% CI, 1.2-3.6) versus those with shorter durations; it also doubled in those treated with oral medications or insulin at baseline versus those treated with diet only. Antihypertensive treatment halved the risk of DR versus no treatment (RR, 0.5; 95% CI, 0.3-0.9) and high systolic or diastolic blood pressure (BP) increased risk. Thus, DR risk increased by 30% for every 10 mmHg of higher systolic BP at baseline (RR, 1.3; 95% CI, 1.1-1.4) or of BP increase from baseline to the 4-year follow-up (RR, 1.3; 95% CI, 1.1-1.4). Diabetic retinopathy risk similarly increased with each 1% of higher glycosylated hemoglobin level at baseline (RR, 1.3; 95% CI, 1.2-1.5). Conclusions: The long-term follow-up of persons with DM in this population of African origin, where disease prevalence is high, identified important potentially modifiable risk factors for DR. Findings suggest that efforts to achieve optimal glycemic and BP control may reduce the vision-threatening complications of DM.