Convergence accommodation.

Steady-state accommodation responses were measured in both eyes as a function of vergence angle and direction of lateral gaze. The measurements were made with a binocular laser optometer. Small speckle patterns were used as fusional stimuli in an otherwise dark field. These patterns have the advantage of providing no blur stimulus to accommodation. Convergence accommodation for vergence angles ranging from 0 to 25 deg was measured for lateral-gaze angles of +32, -32, and 0 deg. The average accommodation of the two eyes was linearly related to vergence angle over the observer's accommodation range but was independent of the angle of lateral gaze. The mean convergence accommodation/convergence ratio for three subjects, in diopters per meter-angle, was 0.9. Our measurements of convergence accommodation using laser-speckle targets are in good agreement with previous studies that used small pupils. Accommodation responses for binocular viewing of letters of a Snellen chart were also measured. When luminance was reduced, night myopia was observed. No similar effect was found for convergence accommodation. Accommodation to a dim target corresponded closely to the convergence accommodation.