To study the relationship between the amount of surgical recession with magnitude and axis of induced astigmatism.
From March 2003 to April 2007, 62 patients with intermittent exotropia who had undergone unilateral or bilateral lateral rectus recession were identified retrospectively. The subjects were divided into two groups: group 1 (34 eyes, 34 patients) with a lateral rectus recession ≤9.5 mm and group 2 (56 eyes, 28 patients) with a recession ≤8 mm. Induced astigmatism was defined as the difference between preoperative and postoperative astigmatism, which was calculated using double-angle vector analysis. Cylinder power and axis of induced astigmatism were analyzed at 1 week, 1 month, and 3 months after surgery.
Larger changes in induced astigmatism were found in group 1 than in group 2 at 1 week after recession (0.8 D cylinder, axis 91° vs. 0.3 D cylinder, axis 88°, Student's t-test, p < 0.01). There was a statistically meaningful correlation between the amount of recession and the cylinder power of induced astigmatism at 1 week after recession (Pearson correlation coefficient r = 0.27, p < 0.01). However, this significant difference between the two groups was not maintained thereafter. Relaxation of astigmatism was observed toward the preoperative value over time in both groups; however, there was a statistically significant difference in the cylinder power of induced astigmatism compared with that of preoperative astigmatism in both groups until the 3-month follow-up (p < 0.01).
The larger recessions had more induced astigmatism during the first week after surgery. However, there was no statistically significant difference in the magnitude of induced astigmatism thereafter between the two groups. Large lateral rectus recession does not seem to produce a sustained astigmatic change compared with moderate recession.