Background/aims To evaluate the surgical outcomes of two-muscle surgery for childhood intermittent exotropia comparing large angles with moderate angles.

Methods We retrospectively reviewed the medical records of 178 children who had undergone bilateral lateral rectus recession (BLR) or unilateral recess-resect (RR) for large-angle (≥40 prism dioptres (PD); group A) or moderate-angle (≥20 and <30 PD; group B) intermittent exotropia with a postoperative follow-up period of 6 months or more. The main outcome measures were postoperative deviation angle and surgical success rate, and the secondary outcome measure was effect/dose ratio. The effect/dose ratio was defined as the corrected angle of deviation at postoperative 6 months divided by the sum of the amount of lateral rectus recession in each eye in BLR and by the sum of the amount of lateral rectus recession and medial rectus resection in RR. Surgical success was defined as alignment between 10 PD of exodeviation and 5 PD of esodeviation both at distance and at near.

Results There was a significant difference in mean angle of deviation at distance throughout the postoperative period (p<0.05). The final surgical success rate was significantly lower in group A than in group B (p<0.05). The effect/dose ratio for both BLR and unilateral RR was significantly greater in group A than in group B (p<0.05).

Conclusions The patients with childhood intermittent exotropia with large angles showed significantly higher rates of undercorrection, though they also showed greater effects of BLR or RR per millimetre (the effect/dose ratio), compared with moderate-angle exotropia.