Purely symmetrical vergence stimuli aligned along the midline (cyclopean axis) require only a pure vergence response. Yet, in most responses saccades are observed and these saccades must either produce an error in the desired midline response or correct an error produced by asymmetry in the vergence response. A previous study (Semmlow, et al. 2008) has shown that the first saccade to appear in a response to a pure vergence stimulus usually increased the deviation from the midline, although all subjects (N = 12) had some responses where the initial saccade corrected a vergence induced midline error. This study focuses on those responses where the initial saccade produces an increased midline deviation and the resultant compensation that ultimately brings the eyes to the correct binocular position. This correction is accomplished by a higher level compensatory mechanism that uses offsetting asymmetrical vergence and/or corrective saccades. While responses consist of a mixture of the two compensatory mechanisms, the dominant mechanism is subject-dependent. Since fixation errors are quite small (minutes of arc), some feedback controlled physiological process involving smooth eye movements, and possibly saccades, must move the eyes to reduce binocular error to fixation disparity levels.

No abstract

The objective of this study is to determine whether the magnitude of a subject's peak velocity is related to a subject's ability to adapt to progressive lenses. Our presumption is that patients fully adapted to progressive additive lenses (PALs) are better motor learners, allowing them to modify their vergence dynamics more readily than patients who could not adapt to PALs. The experiment aims to compare the eye movement dynamic behavior from a 4° double step stimulus which is a 4° step followed by a subsequent 4° step after a 200 msec delay. Eight presbyopes who wear PALs daily and seven presbyopes who could not adapt to PALs participated. The results show that presbyopes adapted to PALs have a significantly greater dynamic ratio of the first to second peak velocity from the two high velocity components stimulated from the double step. This behavior may in part be due to better motor learning abilities.