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Muriel Dysli, Mathias Abegg; Gaze Dependent Vergence Adaptation. Journal of Vision 2015;15(12):825. doi: 10.1167/15.12.825.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The innervational pattern of extraocular muscles that maintain ocular alignment vary with gaze direction, age, and orbital anatomy. A muscle paresis, for example, may cause a misalignment, which is characterized by a gaze dependent deviation of the ocular alignment. Clinically this is termed incomitant strabismus. In this study we aimed at investigating the physiological mechanisms that enable orthophoria, i.e. good ocular alignment, in all directions of gaze. For this purpose we explored the physiological response to vergence stimuli and assessed their directional specificity. Methods: Vergence stimuli of gaze dependent magnitude were used to model image disparity of an incomitant, 'paretic', strabismus. We measured consecutive horizontal vergence responses that were elicited after subjects shifted their gaze from a gaze position without image disparity into a field of view with increased image disparity. Results: We found that repetitive saccades into a field of view with increased image disparity led to a rapid decrease of the phoria level, i.e. the magnitude of ocular misalignment in optically dissociated eyes decreased over time. The decrease was more pronounced in the gaze direction with increased disparity and to a lesser extent in the other gaze directions. Moreover, we confirmed a rapid increase of the vergence velocity over time. The gaze dependent modulation of phoria was found in both, smooth pursuit and saccadic eye movements. Conclusion: Thus an acute gaze dependent change of image disparity, such as may be encountered in new onset paretic strabismus, leads to an increased velocity of the vergence response and an increase of the phoria level with a gaze specific and a gaze independent component. This early adaptive response enables an increased efficacy of binocular vision and an orthophorisation in all directions of gaze in a case of a new onset incomitance.
Meeting abstract presented at VSS 2015
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