Purpose: The purposes of this study are to estimate the 10-year incidence of blindness and visual loss in a diabetic population, examine risk factors for visual loss, and examine temporal trends in rates of blindness and visual loss.
Methods: The design is a population-based cohort study, which includes 891 younger-onset persons with diabetes, 485 persons with older-onset diabetes who are taking insulin, and 502 persons with older-onset diabetes who are not taking insulin and who participated in baseline, 4-year, and 10-year examinations. The main outcome measures are incidence of blindness (visual acuity, 20/200 or worse), doubling of the visual angle, and visual impairment (visual acuity, 20/40 or worse).
Results: The 10-year incidences of blindness were 1.8%, 4.0%, and 4.8% in persons in the younger-onset, older-onset taking insulin, and older-onset not taking insulin groups, respectively. Respective 10-year rates of visual impairment were 9.4%, 37.2%, and 23.9%. Rates for doubling of the visual angle were similar. Doubling of the visual angle was more common in women with older-onset diabetes and in persons with younger-onset and older-onset diabetes who were taking insulin and who had higher glycosylated hemoglobin or proteinuria levels. The presence of macular edema or more severe retinopathy was associated with more visual loss in all three groups. Smoking was associated with visual loss in persons with younger-onset diabetes, and systolic blood pressure was associated in persons with older-onset diabetes who were taking insulin. Rates of blindness and doubling of the visual angle decreased in persons with younger-onset diabetes in the second part of the follow-up. In the older-onset groups, only the rate of blindness declined. These decreases could not be explained entirely by treatment or mortality.
Conclusions: Several modifiable risk factors are associated with loss of vision. Although visual loss is still common in this diabetic population, the incidence of blindness may be decreasing.