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Spatial localization in esotropia: does extraretinal eye position information change?
1Tennent Institute of Ophthalmology, Department of Orthoptics, Gartnavel General Hospital, Glasgow. cliff@weir88.freeserve.co.uk
Purpose:
To investigate the accuracy of spatial localization in children with a specific type of convergent strabismus, fully accommodative esotropia.
Methods:
Two groups of children, with right and left fully accommodative esotropia, respectively, pointed at targets located centrally and eccentrically on a computer touchscreen without being able to see their hands. The size and the direction of the horizontal pointing responses were recorded under two conditions: when their eyes were aligned (wearing spectacles) and when they were squinting (not wearing spectacles). A group of children without strabismus but with hypermetropia were assessed as controls.
Results:
For both fully accommodative groups, the pointing responses to the central target shifted in the direction of the nonsquinting eye when deviations were manifest. No difference was found for the eccentric targets. No difference was found for the hypermetropia group with any target.
Conclusions:
These results are consistent with an alteration in the extraretinal eye position information (efference copy, extraocular muscle proprioception, or both) that is used in spatial localization.