Blindness in a 25-year follow-up of a population-based cohort of Danish type 1 diabetic patients.

Purpose: To assess the long-term incidence of blindness and to evaluate risk factors for blindness in a population-based cohort of type 1 diabetic patients.

Design: Retrospective cohort study.

Participants: A population-based cohort of 573 type 1 diabetic patients, all of whom participated in a clinical ophthalmologic examination in 1981 and 1982 and were followed up for 25 years.

Methods: At the baseline examination in 1981 and 1982, visual acuity, level of retinopathy, maculopathy, hemoglobin A(1) (HbA(1)), proteinuria, smoking habits, and blood pressure were evaluated and related to the subsequent development of blindness. Blindness was defined as present in patients who were registered as members of the Danish Association of the Blind between baseline and January 2007. The Danish Association of the Blind is a voluntary organization open for all patients with a best-corrected visual acuity in the best eye of
Main Outcome Measures: Evaluation of 25-year incidence of blindness, predictors for blindness, and gender-specific incidence rates for blindness.

Results: The 25-year cumulative crude incidence of blindness was 7.5% (men, 8.0%; women, 6.8%; P = 0.61), corresponding to a mortality-adjusted cumulative incidence of blindness of 9.5% (95% confidence interval [CI], 7.1%-12.0%) and an overall incidence rate of blindness of 4.11 per 1000 person-years (95% CI, 3.03-5.59 per 1000 person-years). Blindness was predicted by HbA(1) and maculopathy at baseline. The odds ratio of blindness during follow-up was 1.69 (95% CI, 1.01-2.84) for a 1% increase in baseline HbA(1) and was 6.18 (95% CI, 1.18-32.47) and 8.61 (95% CI, 2.54-29.23) for patients with maculopathy in combination with nonproliferative retinopathy and proliferative retinopathy, respectively. Age and duration at baseline, gender, proteinuria, smoking, systolic and diastolic blood pressure, and visual acuity at baseline were not associated with the development of blindness. Mortality was higher in patients who had become blind (61.0% vs. 42.1%; P = 0.02).

Conclusions: Blindness is still a common complication in type 1 diabetes. Glycemic regulation and the presence of maculopathy are important risk factors for the development of blindness.