Abstract
Recent theoretical arguments (Green et al. (1980) Viston Res. 20, 827–835) predict that young human infants should have large depths of focus compared to adults. If so, optical blur should have relatively little effect on the resolving power of infant subjects. We tested this hypothesis by measuring the influence of optical blur on acuity thresholds in 6-week old infants and adults. Using the forcedchoice preferential looking (FPL) technique, we obtained acuity thresholds for each subject with five different lens powers (piano, −14 D, −3D, +6 D and +14 D). Acuity was differentially affected by lens power in all subjects, with the best acuity found with low power lenses and the worst with the highest power lenses. However, the amount of reduction in acuity produced by high power lenses, both plus and minus, was considerably less for infants than for adults. Although the effects of negative lenses are difficult to interpret without knowing the infants' exact accommodative state, the results with positive lenses support the theoretical predictions.
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