The evaluation of screening policies for diabetic retinopathy using simulation

Aims: To develop a model for evaluating screening strategies and to use it to determine the cost effectiveness of varying the screening method and the screening interval.Methods: A discrete event simulation was designed, validated and run for a population of 500 000. Most parameters were derived from peer-reviewed publications.Results: Standard methods of screening save up to 50% of the potential sight years lost. They give up to 85% of the sight years saved by an idealized gold standard programme using mydriatic seven-field photography reported by an ophthalmologist. The mobile camera, used for annual screening and 6-month follow-up after the detection of background retinopathy, had an estimated cost of £449 200 per year with £2842 per sight year saved. It is less efficient to screen Type 2, rather than Type 1 diabetes mellitus patients, but they contributed to almost three-quarters of the sight years saved.Conclusions: The model can evaluate screening intervals and methods on a national or health authority basis. Results indicate that it appears more cost effective to continue to screen outside an ophthalmology clinic, until treatment is needed. Programmes with annual screening, and more frequent screening for those with background retinopathy, are robust to realistic fluctuations in compliance and screening sensitivity.