Adjustments, voluntary or involuntary, of the crystalline lens of the eye to compensate for the distance of the object of focus from the retina and to keep the image focused on the fovea. The degree of curvature of the lens provides information about the distances of objects, and as such constitutes one of the monocular cues for visual depth perception (another one being motion parallax).
See Depth perception, Eye movements Motion parallax, Oculomotor nucleus, Perceptual development, Stereoscopic depth perception, Visual acuity