Postoperative drifts after adjustable-suture strabismus surgery

OBJECTIVE: To determine the drift patterns and success rates of adjustable-suture horizontal strabismus surgery when patients are aligned to predetermined target angles. DESIGN: Case series. SETTING: University-affiliated tertiary care hospital in Toronto; clinic and office care. PATIENTS: A total of 109 patients aged 15 to 72 years who underwent adjustablesuture strabismus surgery (primary procedure or reoperation) for esotropia or exotropia performed by one surgeon between 1990 and 1994 who were followed for at least 6 months. Their final postoperative angles were in the target ranges of under 4 prism dioptres (PD) for esotropia surgery and 3 PD to 7 PD of esotropia for exotropia surgery. OUTCOME MEASURES: Primary-position alignment before surgery, immediately after surgery or after adjustment of sutures, if needed (final alignment), and at 1 to 2 weeks, 6 to 8 weeks and 6 to 8 months after surgery; size and direction of drift from final alignment after surgery at 6 to 8 months; and rate at 6 to 8 months of reduction of strabismus angle to less than 10 PD. RESULTS: Of the 109 patients 44 had esotropia (17 primary repair [group 1] and 27 reoperation [group 2]) and 65 had exotropia (29 primary repair [group 3] and 36 reoperation [group 4]). Overall, 48 patients (44.0%) required postoperative suture adjustment. The mean drifts from the final postoperative alignments were 1 PD for groups 1 and 2, 7 PD for group 3 and 3 PD for group 4, all in the exotropic direction. The corresponding surgical success rates were 82.4%, 92.6%, 93.1% and 94.4%. Over 6 to 8 months both esotropia groups had approximately equal tendencies to drift in either direction. Both exotropia groups showed almost equal tendencies to drift in either direction away from the mean exotropic shift for the group. CONCLUSIONS: Because of our target alignments, our success rates at 6 to 8 months were high, for both primary surgery and reoperation. In all four patient groups the drift tendencies were symmetric about the mean.