Downshoot in infra-adduction following selected superior oblique surgical weakening procedures for A-pattern strabismus.

PURPOSE

To determine the incidence of postoperative persistent or recurrent, true or pseudo, superior oblique muscle overaction (SOOA) following treatment of A-pattern strabismus by a selective surgical approach; and to seek its cause.

SUBJECTS AND METHODS

Retrospective analysis of the records of 104 consecutive patients with A-pattern strabismus and SOOA treated, with 4 different superior oblique (SO) weakening procedures, selected according to the amount of preoperative anisotropia (in order, smallest to largest): posterior (partial) tenectomy, scleral disinsertion, tenectomy at the insertion and recession with posterior transposition. After exclusions for cause, there were 93 patients who received the same procedure in both eyes. The mean preoperative A anisotropia was 18.30delta+/-8.05delta (range 8delta to 50delta). The mean preoperative SOOA was +2.06 (range +1 to +4).

RESULTS

The mean correction obtained by surgery was 16.20delta+/-8.7delta (88.5% of the preoperative deviation). The mean reduction of SOOA was -1.89 (-91. 7% of the preoperative SOOA, range -75.8% to - 103.1%). During postoperative followup, a pattern of persistence of downshoot in the infra-adducted position of gaze (true/pseudo SOOA) was found in 37. 6% of the cases (28% following tenectomy, 30.7% after recession, 40. 4% after posterior tenectomy and 62.5% after disinsertion). A complication, Superior Oblique Inclusion Syndrome was discovered in two cases.

CONCLUSIONS

Persistence or recurrence of postoperative downshoot in the infra-adducted position is a common finding following any of the SO weakening procedures analyzed in this study. Its occurrence does not seem to be related either to the amount of preoperative SOOA and/or A anisotropia, nor to the amount of A anisotropia correction obtained. Relatively uncontrolled procedures, such as disinsertion, showed the highest incidence of this sequel of surgery.