Purpose: To evaluate the effect on primary position horizontal binocular alignment of superior oblique tenotomy for A-pattern exotropia with bilateral superior oblique overaction using new surgical and anesthesia techniques.
Subjects and methods: We performed intraoperatively adjustable horizontal strabismus surgery under topical anesthesia in 6 cases of A-pattern exotropia. After adjusting the horizontal deviation nearly to orthotropia in primary position, we measured the angle of horizontal deviation in up-, primary, and downgaze positions. This was followed by bilateral superior oblique tenotomy and remeasurement of the horizontal deviation in the same 3 positions. Postoperatively we remeasured the deviation at one day, one month and three months.
Results: There was no immediate change in the horizontal deviation in primary position in 2 of the 6 patients, and 3-8 delta of immediate esotropic shift in 4 of the 6 patients (average 3.3 delta) after bilateral superior oblique tenotomy. At 3 months postop' the small esotropia noted at the immediate postop' measurement became orthotropic. There was a tendency of increased exotropic shift or becoming exotropic in those patients with slight exotropia or orthotropia at the immediate postop' measurement. But these shifts were minimal.
Conclusion: When combined surgery of superior oblique and horizontal muscle is planned for A-pattern exotropia, the effect of bilateral superior oblique tenotomy on the primary position horizontal binocular alignment can be disregarded.