Purpose, To test the hypothesis that the contrast of spectral componen
ts of the retinal image specifies ocular focus and controls reflex acc
ommodation, Methods, Eight subjects viewed a stationary target at 0, 2
.5, and 5 D in a Badal optometer, with longitudinal chromatic aberrati
on (LCA) normal and reversed and in monochromatic (550 nm) light, Acco
mmodation was monitored continuously during 40-s trials, Subjects also
viewed the grating target as it moved sinusoidally (1,5 to 2.5 D) at
0.2 Hz under the same three conditions. Results. Subjects accommodated
relatively accurately at all distances in the normal condition; three
subjects had difficulty accommodating in monochromatic light at 5 or
0 D, and seven subjects could not maintain focus with LCA reversed. Th
e accommodative response differed significantly in the three chromatic
conditions both for stationary and moving targets, Conclusions. Relat
ive contrast of long-, middle-, and short-wavelength components of the
retinal image specifies ocular focus and drives reflex accommodation.