There is a lack of good quality research into the natural history of the target conditions, the disabilities associated with them, and the efficacy of available treatments. This evidence is essential to support a screening programme for a non-fatal condition for which there have been no rigorously controlled trials. An invitation to preschool vision screening carries with it the implicit assumption that screening is going to benefit the child. In the absence of sound evidence that the target conditions sought in the programmes are disabling and that the interventions available to correct them do more good than harm, the ethical basis for such interventions is very weak.