Accommodation to monochromatic and white-light targets

Abstract

Purpose: The objective of the current study was to compare accommodation to targets illuminated with monochromatic light from different regions of the visible spectrum with accommodation to white-light targets.

Methods: One of 10 marrow-band interference filters (430, 450, 470, 500, 530, 550, 570, 590, 630, and 670 nm) was used to produce monochromatic light from a tungsten-halogen source to illuminate a Maltese cross-target in Maxwellian view. Luminance of each monochromatic light was matched by minimum border photometry against a standard white light (3000 K) that was maintained at 200 cd/m2. Chromatic difference of focus of the eye was minimized for all monochromatic targets by the use of an achromatizing lens. A white-light target also was used, and the subject's eye was achromatized or the eye had normal chromatic aberration. The target was moved sinusoidally toward and away from the eye at a temporal frequency of 0.2 Hz over a 1 D amplitude (peak to peak). Accommodation was monitored continuously by an infrared recording optometer, and responses were Fourier analyzed to obtain gain and phase lag at the temporal frequency of stimulation.

Results: Accommodative gain was highest and phase lag was smallest when the target was illuminated by white light in the presence of normal chromatic aberration. The achromatized white-light gain of accommodation was statistically similar to the gain for monochromatic targets, indicating that the presence of chromatic aberration facilitates accommodation. Significant intersubject variability was present in the accommodative tracking ability to monochromatic targets.

Conclusions: Accommodation to monochromatic targets is not as accurate as accommodation to a white-light target, and this effect is related to the presence of ocular longitudinal chromatic aberration for the white-light target.