The effect of monocular versus binocular fixation on accommodative hysteresis

Changes in tonic accommodation were compared under monocular (6 or 10 D) and binocular (6 D/6 MA or 10 D/10 MA) inducing conditions in 26 visually normal young adults. Tonic accommodation was measured immediately before and after an 8 min fixation period. Statistically equivalent increases in tonic accommodation were produced under the two modes and levels of fixation. Even those individuals who showed large (greater than or equal to +0.70 D) monocularly induced changes were equally responsive under binocular fixation conditions. The results suggest that monocularly and binocularly induced accommodative hysteresis effects are similar in magnitude, regardless of the potential presence of vergence-driven accommodation under binocular but not under monocular viewing conditions.