[Efficacy of modified nasal transposition of the split lateral rectus muscle for large-angle exotropia from oculomotor nerve palsy]

Objective: To explore the efficacy of the modified lateral rectus muscle splitting and nasal transposition surgery in treating large-angle exotropia caused by oculomotor nerve palsy and its impact on ocular motility. Methods: Retrospective case series study. Data was collected from patients diagnosed with large-angle exotropia due to oculomotor nerve palsy and treated by modified lateral rectus muscle splitting and nasal transposition surgery at the Tianjin Eye Hospital from January 2020 to October 2023. The prism and Maddox rod method (for unilateral oculomotor nerve palsy patients) and the Krimsky (prism reflection method) (for bilateral oculomotor nerve palsy patients) were used to measure the degree of strabismus. The adduction of the eye was graded. During the surgery, the lateral rectus muscle was split, and the upper and lower halves were transposed nasally to the upper and lower sides of the medial rectus muscle, respectively. Three patients underwent concurrent medial rectus muscle strengthening surgery. Changes in strabismus degree, ocular motility, equivalent spherical degree, and ocular rotation degree before and after surgery were compared. Surgical success was defined as postoperative alignment within 10^△ of orthotropia in primary position by the Krimsky or Hirschberg assessment. Postoperative follow-up was 6 to 12 months. Results: There were 8 patients (9 eyes) with oculomotor nerve palsy, including 2 females and 6 males, with an age range of 1 to 60 years old. At the end of the follow-up period, 7 patients (7 eyes) had a postoperative strabismus degree within 10^△, and 1 patient (2 eyes) was undercorrected. The comparison of the preoperative (-82.78^△± 13.94^△) and postoperative (-6.22^△±8.86^△) strabismus degrees in all eyes showed a statistically significant difference (P<0.05). There was no significant difference in the preoperative [(-0.63±1.94) D] and postoperative [(-0.68±1.84) D] equivalent spherical degrees, and the preoperative (3.96°± 13.79°) and postoperative (6.47°±11.96°) rotation degrees (both P>0.05). The preoperative adduction of the eye [-5.0 (-5.0, -4.0)] was significantly different from the postoperative value [-2.0 (-3.5, -2.0)] (P<0.05). Spearman's correlation analysis showed that the improvement in adduction was not related to the concurrent medial rectus muscle strengthening (r=-0.098, P>0.05), but was related to the preoperative horizontal strabismus degree (r=0.777, P<0.05). No complications such as vision loss, increased intraocular pressure, optic nerve edema, and choroidal detachment occurred in all patients during and after the surgical treatment. Conclusion: The modified lateral rectus muscle splitting and nasal transposition surgery can effectively and safely correct large-angle exotropia caused by oculomotor nerve palsy and significantly improve the adduction function.