Screening for diabetic retinopathy: a relative cost-effectiveness analysis of alternative modalities and strategies.

Diabetic retinopathy is the most common cause of blindness among adults of working age in the UK. If the disease is detected early effective treatment can be provided and this has resulted in calls for a systematic national screening programme. Using data on the screening of 3423 diabetics collected as part of an experimental programme in three UK centres, the relative cost-effectiveness of various screening options is assessed. The paper utilises direct evidence on a number of single modality screening options, including ophthalmoscopy undertaken by general practitioners or ophthalmic opticians, and non-mydriatic photography. With the objective of increasing the sensitivity of screening and using data collected in the study, options based on two further potential screening strategies are modelled and evaluated: combined screening using both ophthalmoscopy and non-mydriatic photography; and selective screening where high-risk diabetics are directly referred to an ophthalmologist and low-risk cases are either left unscreened or are screened by one of the single or combined modality screening options. Given the objective of early detection, effectiveness is assessed in terms of the sensitivity and specificity of the referral decisions of screening options. Both health service and private resource costs of the various screening options are estimated, the latter in terms of travel and the opportunity cost of time. Cost effectiveness is evaluated in terms of the expected cost per true positive case of diabetic retinopathy referred by the screening options. To narrow the choice between the options, those subject to three-way domination with respect to the three choice variables of sensitivity, specificity and expected cost per true positive are excluded. Amongst the remaining options, the choice is dependent on the trade-off between the higher specifics of unselective single modality screening options and the higher sensitivities and lower expected costs per true positive case detected of combined modality and selective screening options.