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November 1975

Structure of the Muscles of the Upper Eyelid

Author Affiliations

From the Laboratory of Vision Research, National Eye Institute, National Institutes of Health, US Department of Health, Education, and Welfare, Bethesda, MD (Drs Kuwabara and Cogan), and the Howe Laboratory of Ophthalmology, Harvard University Medical School, and Massachusetts Eye and Ear Infirmary, Boston (Dr Johnson).

Arch Ophthalmol. 1975;93(11):1189-1197. doi:10.1001/archopht.1975.01010020889012

• The human and monkey orbicularis muscle has fibers that are more uniform in size and structure than those of rectus muscles. They have distinct myofibrils, a moderate number of mitochondria, and a well-developed transverse T-tube system.

The levator muscle also has relatively uniform fibers, but the myofibrils are less distinct than those of the orbicularis. Especially noteworthy is the unusual arrangement whereby Müller muscle arises directly from the undersurface of the levator muscle, causing an intimate intermingling of smooth and striated fibers. Müller muscle then inserts on the tarsus, whereas the levator muscle extends by an aponeurosis into the septa of the orbicularis muscle.

In surgical specimens from patients with ptosis, the levator fibers show varying degrees of abnormality, whereas Müller fibers are normal.

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