Medial–lateral rectus union for long standing complete third nerve palsy: a prospective interventional study from a tertiary eye care centre

Purpose To evaluate the surgical outcomes of medial rectus (MR) and lateral rectus (LR) union in patients with long-standing complete third nerve palsy, with respect to changes in ocular alignment and extraocular motility.Methods This prospective interventional study included 11 patients aged 18–60 years with non-resolving complete third nerve palsy of more than six months’ duration. Patients with partial palsy, multiple cranial nerve palsies, or previous ocular surgery were excluded. All patients underwent MR–LR union, involving longitudinal splitting of the LR into superior and inferior halves, passage of each half beneath the corresponding vertical rectus muscle, and union with the split anterior segment of the MR, while the remaining posterior MR segment was reattached to its original scleral insertion. The primary outcome measure was improvement in ocular alignment. Surgical success was defined as a postoperative residual horizontal deviation of ≤10 prism diopters (PD) and a residual vertical deviation of ≤5 PD in primary position. Secondary outcome measures included changes in ocular motility. Postoperative follow-up was performed until three months.Results The mean preoperative horizontal deviation decreased significantly from 70.45 ± 13.87 PD to 26.36 ± 12.06 PD at three months postoperatively (Friedman test, p < .001). Vertical deviation decreased from 45.91 ± 13.00 PD to 39.09 ± 12.00 PD, without statistical significance (p = .934). Adduction improved significantly from −3.82 ± 0.40 to −2.27 ± 0.65 (p < .001), accompanied by reduced abduction from 0.00 to −1.73 ± 0.79 (p < .001). Surgical success was achieved in one patient (9.1%).Conclusion MR–LR union is a technically feasible procedure that produces significant improvement in horizontal alignment in patients with long-standing complete third nerve palsy. However, vertical correction is limited when performed in isolation, particularly in patients with large baseline vertical deviations. No major complications were observed in this limited prospective series; however, larger studies with longer follow-up are required before definitive conclusions regarding procedural safety can be drawn.