Surface electromyographic assessment of lower eyelid muscle function in ptosis: investigating the role of the orbicularis oculi in scleral show

The purpose of this study is to investigate periocular muscle interactions in patients with involutional ptosis and their relationship to inferior scleral show, using a novel electromyographic biomarker of levator-orbicularis coordination before and after ptosis surgery. In this prospective comparative study, 28 patients with bilateral involutional ptosis and 26 controls underwent surface electromyography (sEMG) of the levator palpebrae superioris and orbicularis oculi muscle. Root mean square amplitudes were recorded during maximal voluntary contraction (MVC) and normalized to calculate the OOM/LPS %MVC ratio. Measurements were obtained preoperatively and at 2 weeks and 6 months postoperatively. Statistical comparisons were performed using one-way and repeated-measures analysis of variance (ANOVA). Preoperative ptosis patients had significantly lower OOM/LPS ratios compared to controls: difference in % MVC ratio=-2.10 (p < 0.0001). Postoperative measurements at both 2 weeks and 6 months showed normalization of this ratio, with no significant difference compared to controls (%MVC = 0.037; %MVC = 0.018, respectively). This study introduces a new functional metric to assess eyelid muscle dynamics. Involutional ptosis is associated with an imbalance between levator and orbicularis activity. Surgical correction restores this balance. Ptosis repair may influence both upper and lower eyelid position and should be regarded as a procedure that restores neuromuscular balance within the periorbital region.