Amblyopia (‘lazy eye’) is the commonest visual disorder of childhood and is caused by an interruption to visual development. Occlusion of the better eye by patching is the mainstay of treatment, so forcing use, of the affected eye. We have little understanding of how much treatment is required for improvement, so occlusion may continue for many months. This is both demanding for the child and family as a whole. Treatment outcome is frequently unsatisfactory. Compliance is often poor, thus we do not know precisely how much treatment the child actually receives or how much is required.