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Daria Ivanchenko, Katharina Rifai, Ziad M. Hafed, Frank Schaeffel; Microvergence eye movements during fixation. Journal of Vision 2020;20(11):1295. https://doi.org/10.1167/jov.20.11.1295.
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© ARVO (1962-2015); The Authors (2016-present)
Even during stable fixation, our eyes make tiny movements called fixational eye movements. In a large fraction of studies, such eye movements were measured in only one eye at a time. While a great deal can still be learned about the impacts of fixational eye movements on visual performance using monocular tracking, such tracking does not aid in understanding additional important mechanisms regarding the integration of visual information from the two eyes. In this study, we used a custom-built video eye tracker to study intraocular correlations of slow fixational drifts. We found that during sustained fixation, the eyes can sometimes drift in opposite directions, particularly along the horizontal dimension. Since these movements are similar to those during convergent eye movements but with much smaller amplitudes, they may be referred to as “microvergence”, in analogy to the commonly used term “microsaccades” for small saccades. Vertical eye positions in the two eyes were more positively correlated, again supporting the notion that the opposite motions in the horizontal direction were related to vergence eye movements. Interestingly, microvergence eye movements were generated independently of visual input: when one or both eyes were covered by infrared transmitting filter(s) that precluded vision in the covered eye(s) but still permitted eye tracking, the spatial-temporal patterns of microvergence eye movements remained similar to when both eyes were uncovered. This suggests that microvergence can be generated by the oculomotor system without the need for visual stimuli. We hypothesize that a possible function of microvergence could be to modulate the statistics of binocular disparities.
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