Pseudo inferior oblique overaction, clinical findings, mechanism, and surgical outcomes.

PURPOSE: To investigate clinical findings of the pseudo inferior oblique overaction (IOOA) syndrome and the outcomes of strabismus surgery and to discuss the mechanisms proposed for this disease.

METHODS

This syndrome is defined by Y pattern strabismus with exotropia in upgaze. There is marked abduction and hypertropia of the adducting eye when elevation is carried out in side gaze, but there is no hypertropia of the adducting eye in horizontal side gaze. Sixteen patients were included and surgery was performed in 14 patients. Success of the surgical intervention was defined as correction of the Y pattern, orthotropia in primary position, upgaze, and downgaze.

RESULTS

Thirteen of the sixteen patients were female. The mean age was 9.6 ± 6.1 years. The mean follow-up time was 14.7 ± 16.9 months. Pre-operatively, 12 patients were orthophoric, and four patients were exophoric (4 to 8 PD) in primary position. In downgaze, all patients were orthophoric. Mean exotropic deviation in upgaze was 25.06 ± 5.9 (18 to 40 PD). Fourteen patients underwent surgery with 2-mm bilateral lateral rectus recession and full tendon supraplacement in seven cases, and 2/3 tendon supraplacement in the other seven patients. The success rate of surgery was 92.8% after the first operation, which reached 100% after a second surgical procedure was performed on one of the patients.

CONCLUSIONS

Strabismus surgery is effective in correcting the Y pattern in patients with pseudo IOOA. A 2/3 tendon supraplacement combined with 2-mm recession of the lateral rectus muscles is the preferred treatment.