Preoperative prism adaptation in acquired esotropia with convergence excess

The prism adaptation test (PAT) is used preoperatively to determine the surgical target angle for acquired esotropia. We assessed the surgical outcomes for children with convergence-excess esotropia (near esotropia greater than distance esotropia by 10 prism diopters [PD] or more) whose target angle was based on the results of the PAT geared to the near deviation.

We reviewed the charts for all of one surgeon's patients who underwent the PAT for near convergence-excess esotropia and who were followed-up for at least 6 months after surgery. Patients who wore prisms were classified as PAT responders (esotropia <= 8 PD at distance and near with four-dot fusion at near) or nonresponders (exotropia at distance or lack of four 4-dot fusion at near). Responders underwent surgery for the adapted angle at near. The nonresponders who had exotropia at distance had surgery for an angle between the near and distance angles. Nonresponders with esotropia angles <= 8 PD at distance and near underwent surgery for the total near deviation.

Fifty-four (83%) of the 65 children were PAT responders. Thirty-nine (72%) of the 54 responders and 6 (55%) of 11 nonresponders had excellent results (heterotropia <= 8 PD at distance and near with four-dot fusion at near). All 13 responders whose angles built with prism had excellent results. Among 61 patients who had an esotropia <= 8 PD at near with prisms preoperatively, only 4 (6.6%) developed overcorrections at distance by the latest follow-up examination; 3 were responders and 1 a nonresponder.

PAT for the near deviation in children who have convergence-excess esotropia is a useful test in estimating the target angle for surgery. Responders whose angles built with prism had a particularly high success rate. Surgery geared to the near-adapted angle has a low risk of creating an overcorrection in the distance regardless of the response to PAT.