Accommodation and chromatic aberration: effect of spatial frequency

Abstract

The longitudinal chromatic aberration of the eye produces color fringes at edges that can have a profound influence on accommodation. We used grating targets to study the influence of spatial frequency on sensitivity to these chromatic cues. A high speed infrared optometer was used to monitor accommodation while the subject viewed gratings in a Badal optometer. Dioptic vergence was modulated sinusoidally (1-3D) by moving a sine wave grating (1-10.5 c/d) toward and away from the subject's eye at 0.2 Hz. Three special lenses were used to modify the chromatic aberration of the eye; giving four stimulus conditions: (1) normal (usual chromatic aberration was present); (2) neutralized (no aberration was present); (3) doubled (aberration was twice as large as usual); and (4) reversed (aberration was opposite to normal). Gain and phase plots show that subjects are most sensitive to intermediate spatial frequencies (3-5 c/d), whether the effects of chromatic aberration are present or not. Furthermore, while subjects display broad individual differences in sensitivity to these cues, such sensitivity seems to be independent of spatial frequency.