Lateral extensions of the Muller muscle
A. D. Morton, V. M. Elner, B. N. Lemke and V. A. White
University of Michigan, Ann Arbor, USA.
OBJECTIVES: To define the lateral extension of the Muller muscle and to
elucidate its involvement in the development and surgical treatment of
Graves (thyroid) eye disease. METHODS: Twelve lateral halves of orbits
exenterated from patients with medial or posterior orbital neoplasms were
fixed, embedded, and step sectioned at 250-microns intervals to produce
histological sections. Gross anatomical dissections of human cadaver heads
were also used to corroborate the histological findings. RESULTS:
Histological analysis revealed that the Muller muscle extended laterally
between the orbital and palpebral lobes of the lacrimal gland in all
specimens. The smooth muscle fibers were found to interdigitate with
lacrimal ducts passing from the orbital to palpebral lobe and to extend
close to the ductal orifices at the conjunctival surface. Gross dissections
confirmed that the Muller muscle accompanied the levator aponeurosis
lateral extension, which is known to pass between the orbital and palpebral
lobes of the lacrimal gland. CONCLUSIONS: Our anatomical findings suggest
that the Muller muscle may contribute to the temporal flare frequently seen
in eyelid retraction associated with thyroid eye disease. They may also
explain the difficulty of treating lateral eyelid retraction in thyroid eye
disease and indicate the need for new surgical approaches for severe
lateral eyelid retraction.
