Histopathological Characteristics of the Levator Muscle in Congenital and Acquired Ptosis With Varying Levator Function

PURPOSE: Levator function (LF) is a key parameter in the evaluation and surgical planning of blepharoptosis; however, it does not always correlate with clinical severity or outcomes. This study aimed to compare the histopathological characteristics of the levator palpebrae superioris (LPS) muscle in congenital and acquired (involutional) ptosis with different LF levels. METHODS: This retrospective study included 38 eyelids from patients with congenital or acquired ptosis who underwent anterior levator surgery. Patients were categorized into 3 groups based on LF: congenital ptosis with LF >5 mm (group 1, n=10), acquired ptosis with LF 9 to 13 mm (group 2, n=12), and acquired ptosis with LF >14 mm (group 3, n=16). Excised levator aponeurosis and muscle tissues were examined histopathologically. Muscle tissue, fat infiltration, fibrosis, edema, and inflammation were evaluated. RESULTS: Muscle tissue was present in all specimens. Fat infiltration differed significantly among groups (P=0.029), being more frequent in groups 1 and 2 compared with group 3 (P=0.041 and 0.039), with no difference between groups 1 and 2 (P=0.218). Severe fibrosis was observed only in group 1, without statistical significance (P=0.193). Edema and inflammation showed no significant differences between groups (P=0.771, P=0.359). Correlation analysis revealed a significant negative correlation between LF and fat infiltration (r=-0.23, P=0.017) and a positive correlation between LF and muscle content (r=0.27, P=0.011) in groups 2 and 3. CONCLUSION: Fat infiltration and muscle content are associated with LF and may partially explain functional variability independent of ptosis etiology.