Impact of unilateral Mueller's muscle conjunctival resection on contralateral upper eyelid position in patients without preoperative Hering's effect.

Purpose: To evaluate the effect of unilateral Mueller's muscle conjunctival resection (MMCR) on the contralateral upper eyelid position in patients without preoperative Hering's effect.

Methods: This retrospective study analyzed 33 patients who underwent unilateral MMCR for mild to moderate ptosis at Shiley Eye Institute, University of California, San Diego. Patients with additional procedures or preoperative Hering's effect were excluded. Margin Reflex Distance (MRD1) was measured using Image J software from standardized digital images. Five masked researchers independently measured MRD1, with the average of the middle three values used for analysis.

Results: The mean preoperative and postoperative MRD1 of the operated eye were 1.20 mm (SD 0.92) and 3.35 mm (SD 0.83), respectively. For the nonoperated eye, preoperative MRD1 was 3.15 mm (SD 0.85) and postoperative MRD1 was 3.28 mm (SD 0.8). There was a statistically significant improvement in the operated eyelid MRD1 ( P < 0.001) but no statistically significant change in the nonoperated eyelid position ( P = 0.704). One patient (3%) experienced an MRD1 drop >1 mm in the fellow eye. Thirty-two patients (97%) had ≤1 mm difference between operated and nonoperated eyelids postoperatively. Interestingly, 18 patients (54.5%) showed a paradoxical increase in contralateral MRD1 (mean 0.66 mm, range 0.02-2.39 mm). All patients achieved acceptable symmetry without requiring additional procedures.

Conclusion: MMCR effectively corrects mild to moderate unilateral upper eyelid ptosis with minimal impact on the contralateral eyelid in patients without preoperative Hering's effect. While the procedure resulted in no significant changes to the contralateral eyelid in 97% of cases, the unexpected finding of paradoxical contralateral lid elevation in over half the patients warrants further investigation.