Influence of Orientation of Exiting Wire of Search Coil Annuli on Torsion Following Saccades

Abstract

Abstract: : Purpose: Previous research has shown that the orientation of the exiting wire from a scleral search coil annulus (nasal in the original annulus, inferior in the modified annulus) can influence the pattern of torsion associated with blinks, presumably due to the upper eyelid touching the wire and rotating the annulus. Here we investigated if coil wire orientation also influenced the pattern of torsion after saccades, and consequently the parameters that determine Listing's plane. Methods: Binocular 3-axis eye movements were recorded to small LEDs at 124 cm distance in three healthy human subjects during a series of predominantly vertical or predominantly horizontal saccades (5-40° in amplitude) at three different (0+20°) azimuths or elevations. Results: With the modified coil, the horizontal component of primary position, as defined by Helmholtz, was similar for horizontal saccades (mean temporal deviation from zero: 2.9°) and vertical saccades (3.3°). With the original coil, primary position was more temporal after horizontal saccades (12.3°) than after vertical saccades (6.1°). The vertical component of primary position was similar with both coils after both horizontal and vertical saccades. Listing's plane was thinner with the modified coil after horizontal saccades (standard deviation of torsion from best-fit plane: 0.71° vs. 1.31°) and after vertical saccades (0.84° vs.1.67°). Conclusions: Our results indicate that measures of eye torsion following saccades using original or modified search coil annuli are different depending upon the horizontal or vertical direction of saccades. There also may be more torsion artifact associated with the original coils, probably related to movement of the wire induced by the moving eyelids.

Keywords: eye movements: saccades and pursuits • eye movements • eye movements: recording techniques