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Müller’s muscle Müller’s muscle is smooth muscle innervated by the sympathetic nervous system. Fibres originate from the undersurface of the levator in the region of the aponeurotic muscle junction, travel inferiorly between the levator aponeurosis and conjunctiva, and insert into the superior margin of the tarsus. With age, fatty infiltration may occur, giving the muscle a yellowish colour. The peripheral vascular arcade of the upper eyelid lies

adherent to the lower border of the anterior surface of Müller’s muscle, just above the upper border of the tarsus, and is apparent during blepharoptosis surgery as a plane of dissection is created between the levator aponeurosis and Müller’s muscle5

fissure with increased sympathetic tone. Approximately 2 mm of ptosis is observed in Horner

syndrome. Sympathetically

innervated smooth muscle fibres are also noted in the lower eyelid and constitute the inferior tarsal muscle. The lower eyelid retractor is a fascial

separated by the inferior oblique muscle. However, an isthmus of fat generally lies anterior to the muscle belly. The inferior oblique muscle takes a bony origin from a shallow depression on the anteromedial orbital floor, directly posterior to the orbital margin and lateral to the nasolacrimal canal. The inferior oblique muscle courses posterolaterally,

passing inferior to the inferior rectus muscle, penetrating Tenon’s capsule, and inserting onto the globe near the macula. Its course makes it susceptible to injury during surgical dissection of the surrounding fat pads.

. The action is to widen the palpebral

Although usually depicted diagrammatically as a discrete

extension from the terminal muscle fibres and tendon of the inferior rectus muscle, originating as the capsulopalpebral head. As it passes anteriorly from its origin, it splits to envelop the inferior oblique muscle and reunites as the inferior transverse ligament (Lockwood’s ligament). From there, the fascial tissue passes anterosuperiorly as the capsulopalpebral fascia. The bulk of the capsulopalpebral fascia inserts on the inferior border of the inferior tarsus. The orbital septum fuses with the capsulopalpebral fascia approximately 5 mm below the inferior tarsal border. The inferior tarsal muscle (Müller’s muscle) lies just

posterior to the fascia and is intimate with its structure. The sympathetically innervated smooth muscle fibres are first noted near the origin of the capsulopalpebral head. In the Asian lower lid, the line of fusion of the orbital septum to the capsulopalpebral fascia is often higher, or indistinct, with anterior and superior orbital fat projection, and over-riding of the pre-septal orbicularis oculi over the pre-tarsal orbicularis. Upper eyelid pre-aponeurotic fat is found immediately

posterior to the orbital septum and anterior to the levator aponeurosis. A central fat pad and a medial fat pad are described in the upper lid, while the lacrimal gland occupies the lateral compartment. The medial fat pad is usually pale yellow or white, and lies anterior to the levator aponeurosis extending superomedial to the medial horn of the levator6

. The central fat pad is yellow and broad. A portion of

the lateral end of this pad surrounds the medial aspect of the lacrimal gland. The lacrimal gland has a firm, pinkish, lobulated structure, in contrast to the soft, yellow intraorbital fat. The anterior border is normally just behind the orbital margin, but involutional changes may lead to prolapse anteroinferiorly, which is prominent on external lid examination. Three retro-septal fat pads are associated with the lower eyelid. The medial and central fat pads are

layer immediately posterior to the orbicularis oculi muscle, the

anterior orbital connective tissue framework.

orbital septum is a multilaminated structure that is part of the

Nerves and arteries Sensory innervation of the eyelids is subserved by terminal branches of the ophthalmic and maxillary divisions of the trigeminal nerve (CN V). The supraorbital nerve exits the orbit through the supraorbital notch or supraorbital foramen. It subserves sensation to the upper eyelid and forehead skin, except for a mid-line vertical strip, which is supplied by the supratrochlear nerve. The infratrochlear nerve, a terminal branch of the nasociliary nerve, supplies the skin and conjunctiva of the medial canthus, the most medial aspect of the eyelids, and the nasolacrimal sac. The sensory supply of the remaining lower eyelid is provided by the

infraorbital nerve and the zygomaticofacial nerve. The zygomaticofacial nerve supplies skin to the lateral lower eyelid, while the palpebral branch of the infraorbital nerve supplies the central lower eyelid skin and conjunctiva. Branches of the facial nerve innervate the muscles of

facial expression. The frontal and zygomatic branches of CN VII innervate the orbicularis oculi muscle; the frontal branch of CN VII innervates the forehead muscles. The orbicularis oculi is innervated by multiple motor branches from the branches of CN VII.

Figure 5 Laser blepharoplasty of the upper lids, as well as transconjunctival

blepharoplasty and resurfacing of the lower lids (A) before and (B) after treatment | November/December 2012 ❚


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