Quantitative Eye Movement Recordings in a Patient with Acquired Bilateral Superior Oblique Palsy Before and After a Bilateral Harada-Ito Procedure

Abstract

Purpose We examined the effects of the Harada-Ito procedure on static and dynamic alignment in an adult with acquired bilateral superior oblique palsy (SOP). Methods 3D eye movements were recorded before and six weeks after a bilateral Harada-Ito procedure. Superior oblique muscle (SOM) size and contractility were assessed with orbital imaging. Results On MRI, the left SOM was smaller than the right. Little contractile thickening was present in down gaze for either eye. Preoperatively, the patient had a hypertropia: 1.9° right hypertropia (at down 20°, left 20°) and 6.4° left hypertropia (at down 20°, right 20°). Postoperatively, the vertical tropia in all positions was < 1°. Listing's primary position rotated toward straight ahead for the RE but was unchanged for the LE. Postoperatively, for 40° upward saccades peak dynamic intrasaccadic extorsion decreased by 2.2–3.2° for both eyes and for 40° downward saccades by 2.3–3.6° for the RE but was unchanged for the LE. Saccade conjugacy improved and post-saccadic drift lessened for all vertical saccades. Conclusions The Harada-Ito procedure produced striking improvements in static and dynamic alignment in bilateral SOP. Some changes were binocular (decreased post-saccadic drift, improved saccade conjugacy, less dynamic extorsion for upward saccades) but others were much greater in the less paretic eye (torsional gradients from up to down gaze, less dynamic extorsion for downward saccades). Both central adaptive and peripheral mechanical changes explain these findings. Our results also imply that the Harada-Ito procedure has more effect when there is residual function of the SOM.