Early diagnosis of diabetic retinopathy by mass examinations in primary health care

Abstract

The general objective of this thesis was to describe a system for fundus photography for early diagnosis of diabetic retinopathy, performed by mobile teams visiting primary health care centres in Stockholm County. Large-scale implementation showed this method to be feasible, acceptable, and popular. Uptake of dilated eye examinations more than doubled from 36.5% to 77.3%; for 97% of patients images could be assessed (3% had media opacities, such as cataract; technical failure for other reasons rarely occurred). The method could also be transferred to another country, and was useful for research into the causes of diabetic retinopathy. As an outcome of diabetes care and eye care, referrals to vision rehabilitation with diabetes and WHO-defined blindness (visual acuity less than 3/60) were used as proxy for new blindness in diabetes. Annual incidence rate fell from 1.2 to 0.63 to 0.33 per 100 000 population when five-year periods from 1981 to 1995 were compared, a reduction by 11 % per year (95% confidence interval 8 to 15%), test for trend p less than 0.001 (Poisson regression analysis).

The method for fundus photography was employed in the city of Tartu, Estonia, in a cohort of insulin-treated diabetes (n=149) followed for three years. Mean HbA1c, measured by the Mono S method in Malmö, Sweden, was 9.3% and was then reduced by 0.5% over three years. Prevalence of diabetic retinopathy was high (76.5%) and comparable to results from the Wisconsin Epidemiologic Study of Diabetic Retinopathy baseline in 1980-1982; for 99 patients diagnosed with diabetes before the age of 30 years in Tartu, the prevalence of any retinopathy was 82%, and 23% had proliferative diabetic retinopathy. Three years later, 37% had undergone photocoagulation, 9% vitrectomy, and 3% had gone blind. Activity of the enzyme SSAO (semicarbazide-sensitive amine oxidase), measured in patients from the Hallunda primary health care centre, was higher in diabetes patients than in controls, higher in the case of retinopathy and stable over time. Urinary concentration of the SSAO substrate methylamine was lower in patients with retinopathy than in those without. SSAO is associated with the development of damage to blood vessels in diabetes and catalyses formation of formaldehyde and hydrogen peroxide in blood vessel walls. Drugs that inhibit SSAO exist; design of more specific inhibitors could open new treatment possibilities.