Aims: The natural history and treatment efficacy of diabetic retinopathy (DR) play important roles in the evaluation of screening. Therefore, the natural history of DR and rates of transition after treatment (including metabolic control and laser photocoagulation) from no diabetic retinopathy (NDR) to blindness were quantified. Methods: We studied a cohort of 795 patients with diabetes mellitus (DM) receiving fundus examination in the ophthalmology out-patient department of one medical centre between 1 January 1990 and 31 December 1992 in Taiwan. Follow-up data until 31 December 1998 were collected by chart review. Two multistate Markov models were proposed to assess the efficacy of the treatment regime in reducing progression to blindness. Results: The average times spent in states (i) no diabetic retinopathy (NDR), (ii) background diabetic retinopathy (BDR), (iii) preproliferative diabetic retinopathy (PPDR), and (iv) proliferative retinopathy (PDR) were 10.86 years, 8.33 years, 1.67 years, and 2.17 years, respectively. Early detection of PPDR may lead to a 60% reduction in PDR and an 83% reduction in blindness. Simulated results based on these parameters show that an annual screening programme, a biennial screening regime and a 4-yearly screening regime can lead to 54% (95% confidence interval (CI): 44-62%), 51% (95% CI: 41-59%), and 46% (95% CI: 36-54%) reductions in blindness, respectively. Conclusions: Assessing the progression of DR following the proliferative pathway in this study suggests that screening for DR is worthwhile and that a 4-year interscreening interval for patients as yet without DR may be justified.
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