ABSTRACT The accommodative response of the eye to low power spherical and sphero‐cyliadrical step stimuli having the same spherical equivalent was measured using a modified Allen‐Carter infrared optometer. It was demonstrated that a subject's response to as little as 0.1 diopter could be detected directly. The subject, fixating a 20/20 letter, triggerred a 1 sec photographic exposure of the oscilloscope trace when he achieved optimum focus. The level of response was obtained by measuring the difference in oscilloscope trace height of two successive exposures, the first with no lens and the second with the randomly presented step stimulus in place. The pattern of response was similar for the two subjects measured, with natural and artificial pupils. In general, for both ‐ 0.25 D and ‐ 0.50 D, a statistically significant lower response level was obtained for sphero‐cylindrical lenses than for their spherical equivalents.
Ludlam et al. (Thu,) studied this question.