AIM: To evaluate the effect of strabismus surgery on retinal vessels calibers with digital color fundus photographs. METHODS: Two hundred consecutive strabismus patients underwent surgery, and 118 patients (female/male, 55/63) who finished 6-month follow-up were finally included in this study. Optic disc-centered digital color fundus photographs of both eyes of all patients were taken prior to surgery and 6mo post surgery. The retinal vascular caliber of 116 operated eyes were measured using the computer program IVAN. The operated eyes were divided into 3 groups according to the surgical methods, recession of one muscle, one muscle recession and one muscle folding, one muscle resection and one muscle recession. The effect of number of altered muscles on retinal vessels was analyzed using statistic software SPSS 16.0. RESULTS: The mean age was 12.4 +/- 8.6y. Averaged central retinal artery equivalent (CRAE) of all patients was 120.31 +/- 23.02 mu M preoperatively, and 122.87 +/- 15.93 mu m six months after surgery. Averaged central retinal vein equivalent (CRVE) was 171.11 +/- 31.73 mu m preoperatively and 175.02 +/- 21.00 mu m postoperatively. There was no significant difference of averaged CRAE (P=0.22) or CRVE (P=0.19) before and after operation. Averaged arteriole to venule ratio (AVR) was 0.71 +/- 0.07 before surgery and 0.70 +/- 0.07 after surgery. Comparison of preoperative and postoperative retinal vessels calibers among different surgical groups did not show significant differences. Also, there was no advantage of rectus muscle folding to muscle resection. CONCLUSION: Up to 6mo after strabismus surgery, the retinal vascular calibers were not altered. No more than two muscles in one surgery are safe for retinal perfusion.