Nomogram for predicting secondary surgery in patients with concomitant exotropia

Concomitant exotropia (CX), a common form of strabismus, often requires surgical correction, yet up to 60% of patients undergo secondary surgery (SS) due to recurrence or residual deviation. Current risk prediction tools remain limited by inconsistent variables and short-term follow-up. This study aimed to develop and validate a nomogram integrating long-term follow-up data to predict individualized SS risk in CX patients. This is a retrospective cohort study of patients with CX who underwent surgery at the Peking University First Hospital between January 1, 2008, and December 31, 2010. Of the 355 CX cases included, 70% were randomly assigned to the training set (n = 248) and 30% to the validation set (n = 107). Demographic and clinical variables were ascertained at hospital admission and discharge and screened using multivariate Cox proportional hazards regression analysis to construct predictive models and generate a one-, three-, and six-year alignment rate nomogram. This nomogram provided an estimate of the risk of SS in patients with surgically treated CX. Internal validation was conducted using the concordance index (C-index) and calibration curve for the training and validation sets, respectively. Four independent prognostic factors were identified: age of onset, refraction, types, and deviation angles one week after surgery entered into the nomogram. The proposed nomogram showed favorable discrimination and accuracy in the training and validation sets. The C-indexes of the training and validation sets were 0.83(95%CI:0.71 ~ 0.95) and 0.80(95%CI: 0.70 ~ 0.89), respectively. The proposed nomogram may serve as a predictive tool for prognostic evaluation of CX surgery.