Effect of nearpoint stress on the horizontal forced vergence fixation disparity curve.

The effect of nearpoint stress on the forced vergence fixation disparity curve was investigated directly. Data gathered from asymptomatic subjects with normal binocular vision showed that fixation disparity was not influenced by 25 min of continuous reading. Further investigation using symptomatic subjects with large fixation disparities or steep forced vergence curves showed that the nearpoint reading task had a significant effect on the curves of these subjects. Clinical implications and a possible physiological substrate are presented.