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R. Suryakumar, E.L. Irving, W.R. Bobier, T.L. Simpson; Saccade Dynamics During Symmetrical and Asymmetrical Vergence . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1974.
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Purpose: Studies (1) show that saccades associated with an asymmetrical vergence (ASV) show lower rates of peak acceleration compared with purely conjugate saccades (CS) to distant targets. This study investigated whether the symmetry of the vergence response and the saliency of the target impacted on the amplitude/peak velocity relationship of the saccades, which punctuate vergence responses. Methods: Binocular eye position was recorded continuously from 4 normal subjects (mean age 25±3.5 yrs) at 120Hz using a video based eye tracker (ELMAR 2020). The distant target at 2m consisted of a white square on a dark surround and the near target provided either a strong contour (LED light on a dark background) or a weak contour (diffuse pinhole of light). Subjects made symmetrical vergence (SV) and then ASV (targets lined up with OD and then OS) between distance and near every 5 seconds for a period of 1 minute. Subjects also made right and leftward CS to 2m distant targets over a range of 2 – 10 degrees. All saccades in SV, ASV were identified in the convergent and divergent traces and their amplitudes/peak velocities were compared to CS. Results: As expected, the saccade velocity for given amplitude during ASV (convergent and divergent) was significantly slower (ANOVA, p<0.05) than corresponding CS. The effect was more evident in the un-aligned eye. This was also found in SV (ANOVA, p<0.05). The ‘diffuse’ near target setting decreased the frequency of large amplitude saccades during SV and decreased the number of saccades during ASV (convergence). However, the amplitude/peak velocity relationships in SV or ASV were not significantly changed (F test, p>0.05) from the strong contour target. Conclusions: With amplitudes matched, velocities of saccades are reduced regardless of symmetry of vergence response. Weakening the contours of a near target reduced the number of saccades in ASV and the frequency of large amplitude saccades in SV. However, the amplitude/peak velocity relationships were unchanged when compared to LED view.(1) Ramat et al. Exp. Brain Res.1999; 129:500-10.
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