The role of stereopsis and early postoperative alignment in long-term surgical results of intermittent exotropia.

Despite the presence of good stereopsis, surgically corrected intermittent exotropes may show a gradual outward shift with time. The purpose of this study was to identify early factors that influence the success of corrective surgery. Sixty-seven consecutive patients treated surgically for intermittent exotropia (age range 1.9 to 76 years) constituted our final sample. Sensory status was evaluated with the Titmus stereotest. A successful surgical result was defined as phoria or intermittent tropia of +/- 10 prism dioptres or less for near and distance with maintained or improved stereopsis, 6 months or more after surgery. The average postoperative follow-up period was 3.3 (range 0.5 to 11) years. Good stereopsis (60 seconds of arc or better) was present in only 42% of the patients preoperatively and 61% postoperatively. The overall surgical success rate was 60%. Early overcorrection, defined as an esodeviation present within the first 4 weeks after surgery, caused a significant improvement in the success rate, to 79% (p = 0.03). Poor preoperative stereopsis combined with early overcorrection resulted in a further significant improvement in the surgical success rate, to 92% (p = 0.07). This suggests that poor preoperative stereopsis does not necessarily preclude, and may enhance, long-term alignment stability postoperatively. We suggest that it is peripheral rather than central fusion that keeps the eyes well aligned after surgery and prevents recurrence of the exodeviation.