Abstract
Abstract: :
Purpose: The Harada–Ito procedure is used to treat excylotropia but how it affects eye movements is unknown. Here we examined the effect of this procedure in an adult with bilateral superior oblique palsy (SOP) and bilateral extorsion. Methods:We recorded eye movements before and one month after a bilateral Harada–Ito procedure (the superior oblique tendons are split and the anterior fibers are advanced anteriorly and laterally). Binocular scleral search coils were used to measure three–axis eye movements during 40° vertical saccades in 20° adduction, midline, and 20° abduction. Changes in static torsion during fixation and peak velocity, peak acceleration, and peak dynamic torsion (torsion beyond that expected from any change in static torsion) during saccades were determined. Results: Before surgery, there was little vertical phoria except for 1.9° right hyperphoria at down 20°, left 20°; 2.5° left hyperphoria at down 20°; and 6.4° left hyperphoria at down 20°, right 20°. After surgery, the vertical phoria in all positions was <1°. For the right eye, the post–op change in static torsion was 7–10°extorsion in up gaze and 7–10° intorsion in down gaze. For the left eye, the pattern was the same but the amplitude was considerably less (<3°). After surgery, for both eyes, peak vertical saccade velocities and accelerations increased 12 to 17%. Vertical saccade velocities increased 76 ± 19°/s for up saccades (P=0.0002) and 38 ± 16°/s for down saccades (P=0.0021). Peak vertical saccade acceleration also increased: 2500 ± 1300°/s2 for up saccades (P=0.0054) and 1500 ± 710°/s2 for down saccades (P=0.0029). The post–op change in dynamic torsion for up saccades was 2.2–3.2° intorsion for both eyes. For down saccades, the change in dynamic torsion was 2.3–3.6° extorsion for the right eye but was <0.2° for the left eye. There was little difference in these parameters whether the vertical saccades were made in adduction or in abduction. Conclusions: Vertical saccade velocity and acceleration and torsional alignment were considerably improved following surgery. Changes in vertical eye alignment, vertical saccade dynamics, static torsion, and dynamic torsion were not well correlated. Changes in dynamic and static torsion occurred largely independently of horizontal eye position. Thus, simply altering the insertion of only part of the superior oblique tendons leads to widespread changes in ocular alignment and saccade dynamics.
Keywords: eye movements: saccades and pursuits • strabismus: treatment • binocular vision/stereopsis