ASYMMETRICAL VERTICAL PHORIAS INDICATING DISSOCIATED VERTICAL DEVIATION IN SUBJECTS WITH NORMAL BINOCULAR VISION

We measured the symmetry of phoria angles in six normal subjects. Subj ects were selected on the basis of good visual acuity and stereopsis, normal binocular eye alignment and, apart from mild refraction errors, absence of ocular abnormalities. They were instructed to look at a wo rd on a reading chart at 2 m distance. Each measurement consisted of f ive subsequent intervals of 5 s duration. During these five intervals viewing was binocular, with the right eye only, binocular, with the le ft eye only, and binocular, respectively. Each experiment consisted of twelve measurements. Eye movements were measured with scleral coils s uited for measuring in horizontal, vertical and torsional directions. Five out of six subjects displayed an asymmetrical vertical phoria; on e subject showed an alternating hyperphoria; four displayed a left ove r right vertical phoria that was largest for left eye occlusion. Only one subject showed a symmetrical vertical phoria. Both the size of the vertical phorias and the size of the asymmetries in these vertical ph orias were very small: on average 0.16 +/- 0.01 and 0.17 +/- 0.01 degr ees, respectively. The direction of the vertical phoria asymmetries (t he largest left over right was found with left eye occlusion) and the fact that asymmetries were found more often in vertical than horizonta l and torsional phorias suggest that these asymmetries are related to dissociated vertical deviation. These results suggest that dissociated vertical deviation, often observed in subjects with a disruption of b inocular vision early in life? reflects the enhancement of a phenomeno n that is present in normal subjects as well. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.