INSTABILITY OF OCULAR TORSION DURING FIXATION - CYCLOVERGENCE IS MORESTABLE THAN CYCLOVERSION

We investigated spontaneous variation of binocular torsion. Variation was expressed as SD of torsional eye positions measured over periods u p to 32 sec. Subjects viewed a single dot target for periods of 32 sec . In half of the trials a large random-dot background pattern was supe rimposed on the dot. The movements of both eyes were measured with scl eral induction coils. Spontaneous torsional movements were largely con jugate: cyclovergence was much more stable than cycloversion. This dif ference was not due to roll head movements. Stability of cyclovergence was improved by the background pattern. Although overall stability (S D of position) of cycloversion was unaffected by a background, the bac kground induced or enhanced a small-amplitude torsional nystagmus in 3 out of 4 subjects. We hypothesize that the difference in stability of cycloversion vs cyclovergence reflects the greater importance of tors ional retinal correspondence, compared to absolute torsional position. In two subjects we found evidence for the existence of cyclophoria, m anifested by systematic shifts in cyclovergence caused by the appearan ce and disappearance of the background.