The Levator Aponeurosis Contains Smooth Muscle Fibers: New Findings in Caucasians

PURPOSE: To examine the microscopic structure of the upper eyelid of Caucasians, in particular looking for evidence of the presence of smooth muscle fibers and the microscopic nature of the levator aponeurosis. METHODS: Full-thickness sagittal sections of central upper eyelids from 11 postmortem upper eyelids of 7 Caucasians (age range 78-101 years at death; mean age 87.7 years) were examined. The samples were stained with Masson trichrome and were microscopically examined for the presence of smooth muscle fibers and to determine whether the levator aponeurosis comprised one or more layers. RESULTS: All of the samples contained smooth muscle fibers, which were located posteriorly. Evidence of a clear double-layer structure was found in only 1 sample; the other 10 samples demonstrated a single monolayer, which was not reflected to the orbital septum but continued distally. CONCLUSIONS: In this series of upper eyelid specimens of Caucasians, all aponeuroses contained smooth muscle fibers, the distribution of which was more concentrated posteriorly, identical to previous findings in Asian eyelids and suggestive of a possible common mechanism of eyelid tension regulation between races. Most of the levator aponeuroses examined had evidence of a single monolayer only; this represents a further absolute difference in the microanatomical structure of the upper eyelids between Caucasians and Asians.