Two factors affecting saccadic amplitude during vergence: the location of the cyclopean eye and a left-right bias.
Saccades occurring during vergence have been reported to differ in amplitude depending on whether the saccade drives the eyes leftward or rightward. Furthermore, this difference varies in degree and direction among individuals. We examined two explanations of the variation--that it is the result of the cyclopean eye being nearer to one eye, and that it is the result of a pervasive bias, within an individual, to make larger saccades either leftward or rightward. Examination of the saccades of 14 subjects, recorded during both divergent and convergent movements that required leftward or rightward saccades, shows that neither explanation alone provides an adequate account of the differences observed. However, statistical analysis (ANOVA) indicates that almost 60% of the total variation in the observed saccadic amplitudes is related to the two explanations taken together. We speculate that both influences act on the saccade in a given individual, and that the amplitude manifested depends on the relative magnitudes of the two influences within that individual.
D000065:Accommodation, Ocular; D000704:Analysis of Variance; D005133:Eye Movements; D006801:Humans; D008954:Models, Biological; D012438:Saccades