To evaluate surgical outcome in the patients with acquired nonaccommodative esotropia who were operated based on a short prism adaptation test (PAT) and to determine the subgroup of patients more responsive to PAT.

The study was Prospective interventional cases series. Twenty eight patients with acquired non-accommodative esotropia were enrolled in this clinic-based study. The patients wore Fresnel trial lenses based on the results of alternate prism-cover testing. With the Fresnel prism in place, alignment was measured after 20 minutes. If the deviation increased, the power of prism would increase to neutralize this angle. The test was repeated every 20 minutes to achieve motor stability. The patients were classified as either prism responders (if the angle of deviation increased >10 ∆ compared to the entry angle) or prism non-responders. All patients underwent bilateral medial rectus muscle recession. Patients were operated based on the enhanced angle if they were prism responders.

Fourteen patients (50%) were prism responders and 14 (50%) were classified as prism non-responder. After 6 months, 100% of patients in the prism responder group and 92.9% in the non-responder group were aligned within 8∆ of orthotropia at distance and near fixation. None of the patients with an entry angle >30∆ were prism responder

A short PAT with an endpoint motor stability in patients with acquired nonaccommodative esotropia is associated with a good surgical outcome and a low rate of over- and undercorrection. PAT might not be necessary for patients who present with an angle of deviation >30∆.