Surgery in the prism adaptation study: accuracy and dose response. Prism Adaptation Study Research Group.

Three hundred twenty-two patients underwent strabismus surgery for acquired esotropia according to a rigid protocol in the Prism Adaptation Study (PAS). This report describes the PAS surgical technique and the methods used to evaluate and assure adherence to the surgical protocol. We present analyses of the discrepancies between the amount of recession surgery planned by the surgeon and the amount of recession estimated by the masked graders from documentary photographs. In 74% of patients, the total discrepancy (combined from both medial rectus operations) was 1 mm or less. There was a distinct trend for masked graders to estimate larger recession amounts than were dictated by the protocol and claimed to be done by the surgeon. In 24% of patients, the masked graders estimated that the recession was more than 1 mm greater than that claimed by the surgeon, while in 2%, the graders estimated that the surgery was more than 1 mm less than planned. Of the 74 patients for whom the graders' estimated total recession was more than 1 mm greater than the amount planned by the surgeon, 88% were successful. Of the six patients for whom the graders' estimated total recession was more than 1 mm less than the amount planned by the surgeon, five (83%) were successful. We propose new surgical tables for patients with acquired esotropia. Enhanced amounts of recession appear to be necessary to decrease the rate of undercorrection for each group of patients.