Congenital esotropia and amblyopia are treated during the 'sensitive period' of brain-eye development. Not all children require spectacles for treatment of these conditions but when refractive errors are present, correct and properly fitting spectacles play an important part. This prospective survey shows that one-third of the under three-year-old children wearing spectacles require surgery for esotropia, and that one-third of all children under eight years of age wearing spectacles need amblyopia treatment. It is uninterrupted treatment in these age groups that produce results. Approximately 50% of children wearing spectacles in the four-year-old and under group need a second or third pair of spectacles within a 12-month period. If these spectacles become unsuitable because of dense scratches, changed refraction or poor fit because of increasing P D, then the treatment is interrupted and the visual acuity is likely to regress. Many families cannot afford a second or third pair of spectacles within the 12-month period and hospital benefit funds often will not help. The treatment is interrupted. This financial hazard must be overcome.