CHROMATIC ABERRATION AND OCULAR FOCUS - FINCHAM REVISITED

Longitudinal chromatic aberration of the eye (LCA) produces ''color fr inges'' at edges that specify focus. Fincham [(1951) British Journal o f Ophthalmology, 35, 381-393] concluded that these chromatic effects w ere important for accommodation, but most investigators disagree. We m onitored accommodation in 25 subjects while they viewed a sinusoidally moving target (1.5-2.5 D at 0.2 Hz) in a Badal optometer. The target was monochromatic (590 nm with 10 nm bandwidth), or white (3000 K) wit h LCA normal, neutralized or reversed. Sensitivity to the effects of L CA is profound and widespread. Gain decreases substantially and phase- lag increases when LCA is eliminated, and reversing the aberration sev erely disrupts accommodation. The ordered arrangement of spectral foci produced by LCA seems to be a fundamental aspect of the stimulus for ''reflex'' accommodation.