A transverse study of the monocular, steady-state accommodation response/stimulus curves for 49 normal subjects with ages between 17 and 49 years shows that the slope of the curve reduces only slowly with age up to about 40 years and then declines rapidly as complete presbyopia is approached. Such behaviour appears to result from the accommodation system changing its characteristics with age to make optimal use of the available objective amplitude of accommodation and the depth-of-focus of the eye.