The vitreous chamber decreased in depth about 0.12 mm as accommodative demand increased from 0.2 to 7 D in nine accommodative steps. The depth decreases matched movement of the posterior lens surface toward the retina. Accommodation caused no significant increases in axial length compared to cyclopleged controls. These results do not favor the active role for the vitreous in accommodation proposed by Coleman in 1970. Computer analysis of A-scan interval counts demonstrated that multiple retinal complex peaks might erroneously point to vitreous or axial lengthening. About 30% of total lens thickening during accommodation was accounted for by posterior lens surface displacement.