Eye Position Changes Under General Anesthesia In Infantile Strabismus: Differences Between Esotropia And Exotropia

Purpose: To study the different trends of eye position changes under narcosis in Infantile Intermittent Exotropia (IXT) compared to Infantile Esotropia (ET). To discuss the possible causes of the difference. Methods: Twenty-nine patients, aged 2 to 15 years, undergoing surgery for infantile concomitant strabismus at University Eye Clinic of Bologna, between January 2017 and December 2019, took part in this prospective study. Of them, 13 had basic or simulated divergence excess IXT and 16 had ET. Eye position was measured preoperatively and under general anesthesia with a modified Paliaga Test for the measure of interlimbal distance (ILD). In IXT patients the prolonged occlusion test was performed preoperatively. Neuromuscular blocking agents were not used to induce general anaesthesia. Results: In IXT patients the difference between preoperative and intraoperative ILD was not statistically significant (Wilcoxon, p>0.05), and showed a great variability, as under narcosis ILD decreased in 38.46%, did not change in 30.77%, and increased in 30.77% of patients; while in ET patients it increased under narcosis, with a statistical significance (Wilcoxon, p=0.002). Conclusion: Differences in the determinants of the ocular deviation may be suspected in ET and IXT, particularly regarding the role of esotonus, that is the baseline innervation to the extraocular muscles which opposes the position of rest in the awake state and which is suppressed under narcosis. While esotonus is increased in ET, it could be even decreased in IXT where other innervational phenomena, like active divergence, may be involved in determining the deviation.