COSTS AND METHODS OF PREVENTIVE VISUAL SCREENING AND THE RELATION BETWEEN ESOTROPIA AND INCREASING HYPERMETROPIA

Atkinson has shown that early correction of hypermetropia reduces the incidence of esotropia. If esotropia is reduced by prescribing glasses early, the rate of esotropia-induced amblyopia can be similarly reduc ed; this would have important economic consequences. We have studied ( 1) how costs compare to benefits in early visual screening, (2) how vi deorefraction as used by Atkinson compares to retinoscopy, and (3) whe ther esotropia is more likely to occur in children who have increasing as opposed to decreasing hypermetropia. The costs of the study so far have been high. It was exceedingly difficult to get all infants invit ed, come to the clinic and examined. Videorefraction did not compare f avourably with retinoscopy in terms of costs and precision, whereas th e amount of skill and time needed was approximately equal. The third q uestion, whether esotropia is more likely to occur in children who hav e increasing as opposed to decreasing hypermetropia, arose from the co ntroversy whether, in the general population, refraction increases or decreases during the first years of life. We found that papers reporti ng a decrease of hypermetropia in early childhood were studies of larg e cross-sections of the general population, whereas papers that report ed an initial increase originated from ophthalmological practices or s trabismus departments. These conflicting results could be reconciled b y assuming a population bias: if esotropia is more likely to occur in children with increasing hypermetropia, children with increasing hyper metropia will preferentially be seen by ophthalmologists. It seems nat ural that children with increasing hypermetropia are more likely to sq uint, because additional accommodation, needed to overcome increasing hypermetropia, will inevitably confer additional convergence. This rel ationship has meanwhile been confirmed by others.