Superior tarsal muscle

The superior tarsal muscle (a.k.a. Müllers muscle), is a thin sheet of smooth muscle located in the upper eyelid. It lies deep to the levator palpebrae superioris and extends from the undersurface of the levator muscle and its aponeurosis to the superior border of the superior tarsal plate.

Superiorly, Müllers muscle arises near the point where the levator palpebrae superioris transitions into the levator aponeurosis. Inferiorly, it inserts into the superior margin of the superior tarsus. Through this attachment, it contributes a small but important component of upper eyelid elevation.

The superior tarsal muscle is composed of involuntary smooth muscle fibres and receives sympathetic innervation from postganglionic fibres arising from the superior cervical ganglion. Functionally, it assists the levator palpebrae superioris in elevating the upper eyelid and helps maintain the normal resting position of the eyelid.

Clinical correlate

Clinically, interruption of the sympathetic supply to the superior tarsal muscle, as occurs in Horner syndrome, produces mild ptosis due to loss of smooth muscle tone in the upper eyelid.