Purchase this article with an account.
E.D. Cornell, I.S. Curthoys, H.G. MacDougall; Asymmetrical Fixations Following Vergence Eye Movements to Iso–Vergent Targets . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2487.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
In 1995 Collewijn, Erkelens and Steinman reported on the dynamics of version and vergence eye movements as subjects redirected their eyes both in distance and direction, requiring eye movements with properties of both vergence and saccade. In this report they commented on "ambiguous vergence eye movements" that were made by at least 2 of the 5 subjects during changes to iso–vergent targets, usually requiring 5o of vergence, but occasionally 10o. These movements were not observed for larger or asymmetrical movements. We have examined the recordings from 33 subjects with normal binocular vision and ocular motility, most of whom volunteered for a previous study that required them to make horizontal vergence changes to targets situated on the mid sagittal plane, to find evidence of asymmetrical fixations in order to further identify their characteristics.
Eye movement recordings of 34 subjects that were made using a video based system were examined for evidence of the "ambiguous vergence eye movements" similar to those described by Collewijn, Erkelens and Steinman
Of the 30 subjects with little or no heterophoria, six (20%) showed steady asymmetrical fixations resulting in significant vergence errors without diplopia. Four other subjects with moderate heterophoria showed similar fixations that were consistent with their heterophoria, three exophoric subjects tended to maintain fixation on the far target with one eye and shift the other eye from far to near, and one esophoric subject tended to maintain fixation on the near target with one eye and shift the other eye from far to near. Conjugate movements showed equal excursions of each eye. No subjects reported diplopia.
Static asymmetries without diplopia following binocular changes of fixation to iso–vergent targets are relatively common under experimental conditions. The resulting disparities of up to 7.5o are well outside the limits of Panum’s fusional space and confirm previous reports of tolerance to disparity without diplopia in normal subjects.
This PDF is available to Subscribers Only