Journal of Pediatric Ophthalmology & Strabismus • Vol. 50, No. 1, 2013 53 INTRODUCTION Congenital esotropia is the most common eye deviation with an incidence of 1% to 2% of the population 1 and is defined as constant esodeviation with onset prior to 6 months of age. The treatment of choice is surgery, and there is a possibility of reopera- tion in 19% to 69% of patients according to different reports. 1-6 The risk factors for reoperation are not well known, but age younger than 15 months at first sur- gery, congenital esotropia greater than 30 or 50 prism diopters (PD), accompanying inferior oblique muscle overaction, dissociated vertical deviation, latent nys- tagmus, amblyopia, and positive family history of esotropia have been introduced as the risk factors of reoperation, with no consensus on all of them. 1-3 Although it is generally accepted that final align- ment should be achieved before 2 years of age, 1 some surgeons have recommended surgery at a younger age as soon as possible after the onset of stable esotropia for better sensory results. In addition, surgery before 15 months of age has been reported to be associated with higher frequency of reoperation, 1,6 possibly due Purpose: To determine the prevalence rate and related risk factors of reoperation among patients with con- genital esotropia. Methods: One hundred fifty-seven children with con- genital esotropia were divided into two groups after at least one operation: children with deviation within 10 PD (n = 89; success group) and those with deviation great- er than 10 PD or history of reoperation (n = 68; failure group). The relationship of risk factors such as age at first operation and primary congenital esotropia of less than 30 or more than 50 PD and accompanying factors such as inferior oblique muscle overaction (> +1), dissociated vertical deviation, lateral rectus muscle underaction, and A-V pattern with reoperation were studied. Final sensory status of children 5 years and older was evaluated by Worth 4-dot and Titmus tests. Results: Reoperation was indicated in 32.4% of chil- dren who had residual esotropia greater than 15 PD after 3 months following their first operation. Congen- ital esotropia greater than 30 PD (P = .002) and lateral rectus muscle underaction of -1 to -2 (P < .005), were statistically different between the two groups. Initial operation at younger than 3 years was more likely to achieve gross stereopsis in children 5 years and older (P = .032). Conclusion: Congenital esotropia greater than 30 PD and lateral rectus muscle underaction were found to be risk factors of reoperation. [J Pediatr Ophthalmol Strabismus 2013;50:53- 59.] ABSTRACT The Prevalence of Reoperation and Related Risk Factors Among Patients With Congenital Esotropia Zhale Rajavi, MD; Ahmad Ali Ferdosi, MD; Mina Eslamdoust, MD; Mehdi Yaseri, PhD; Narges Haftabadi, MS; Setareh Kroji, MS; Kourosh Sheibani, MD From Ophthalmic Research Center (ZR, AAF, ME, MY), Clinical Research and Development Center (KS) of Imam Hossein Medical Center (ZR, AAF, ME, NH, SK), Shahid Beheshti University of Medical Sciences; and the School of Public Health and Institute of Public Health Research (MY), Tehran University of Medical Sciences, Tehran, Iran. Originally submitted February 7, 2012. Accepted for publication July 26, 2012. Posted online September 11, 2012. The authors have no financial or proprietary interest in the materials presented herein. Address correspondence to Zhale Rajavi, MD, 5th Floor, No. 6, 3rd Sharestal, North Pesian, Moghadas Ardabili St., Vali-ye-Asr Ave., Tehran 19868- 66814, Iran. E-mail: zh_ra2000@yahoo.com doi: 10.3928/01913913-20120804-11