Maximum motor fusion combined with one-hour preoperative prism adaptation test in patients with acquired esotropia

Preoperative prism adaptation and the maximum motor fusion test reduce the risk of postoperative undercorrection, overcorrection, and bifocal requirements in acquired esotropia. The purpose of our study is to determine the efficacy of the maximum motor fusion test followed by a short prism adaptation test in patients with acquired esotropia undergoing bilateral medial rectus muscle recession.

We undertook a retrospective review of 29 subjects with acquired esotropia without history of amblyopia, previous strabismus surgery, use of bifocals, pattern anisotropia, dissociated vertical deviation, or oblique muscle dysfunction. All subjects underwent bilateral medial rectus muscle recessions based on the distance angle of deviation measured with the maximum motor fusion test followed by prism adaptation test. Alternate prism and cover testing was performed after 1 hour of prism adaptation to determine the angle of deviation for surgical correction.

The age at surgery was 4.5 +/- 1 years. The preoperative angle of deviation at distance was 20.4 +/- 4.2(delta). It increased to 36.2 +/- 4.2(delta) after the maximum motor fusion test followed by 1 hour of prism adaptation testing. The final preoperative angle of deviation post motor fusion test-prism adaptation test was significantly larger than the initial angle of deviation (p < 0.0001). The final postoperative deviation at distance was 1.3 +/- 3.3(delta), and 5.2 +/- 1.5(delta) at near. Postoperative follow up was 18 +/- 2.6 months (range, 13-24 months).

The combination of maximum motor fusion and preoperative prism adaptation allowed increased amounts of medial rectus muscle muscle recession, decreasing the risk of postoperative undercorrection without increasing the risk of overcorrection.