To report the dose-response relationship of adjustable Harada-Ito surgery, and postoperative stability of cyclodeviation.

Retrospective cohort study.

Twenty patients underwent a unilateral adjustable Harada-Ito advancement of the anterior fibers of the superior oblique tendon, with or without resection. The surgical dose was calculated as resection plus advancement plus adjustment. Cyclodeviation was measured using double Maddox rods at preoperative and postoperative time points. We assessed dose effect by calculating change in cyclodeviation from preoperatively to postadjustment and evaluated the dose-response relationship by Spearman rank methods. Postoperative stability of cyclodeviation was assessed by comparing postadjustment measurements with 1-day and 6-week measurements, and also 1- and 5-year measurements, when available.

Change in cyclodeviation from preoperatively to postadjustment ranged from 7 to 20 degrees of incyclo effect. There was a dose effect of 1.3 degrees per mm (r_s = 0.52, P = .019). Postoperative incyclodeviation unwound a mean of 3.6 degrees ± 2.5 degrees between postadjustment and day 1. Overall change between postadjustment and the 6-week window was 6.5 ± 2.9 degrees in an excyclo direction. Unwinding continued with a mean change of 0.2 ± 2.6 degrees between the 6-week and 1-year windows, and of 0.4 ± 2.1 degrees between 1-year and 5-years windows.

Adjustable Harada-Ito advancement of the anterior fibers of the superior oblique tendon has a dose response of 1.3 degrees per millimeter, but its effect regresses over time. Based on our data, an immediate postoperative target incyclodeviation of 7 degrees is reasonable.