What should policy makers do with systematic reviews that fail to find evidence of effectiveness for interventions currently provided in the NHS? Is no evidence of effectiveness sufficient evidence of no effectiveness? The systematic review process has made great progress in minimising the influence of personal bias in the selection and critical appraisal of evidence. By bringing together in one place and critically appraising all the relevant studies, these reviews can show the fragility of the evidence on which some current practice is based.

Policy makers in the NHS take the results of these reviews seriously and expect to be able to act on their findings. But clinicians argue that it is wrong to close down a service, which might be doing good, just because the research evidence of effectiveness is poor. The review of pre-school vision screening commissioned by the NHS Health Technology Assessment Programme1 raises this dilemma and presents policy makers with a difficult decision. This report’s most startling finding was that the reviewers could not identify any robust studies showing that amblyopia (the main target condition of pre-school vision screening programmes2) causes any problems to children or adults. One researcher who tried to find performance differences between amblyopic students (as opposed to people blinded in one eye in adulthood or blindfolded in one eye for the purpose of an experiment) and students with monocular refractive errors was not able to document disabilities that he considered likely to affect everyday life.3 Health professionals have always assumed that reduced vision in one eye must cause problems, and in occupational health services health professionals have been responsible for the development of policies that exclude people …