Anatomical aspects of lower eyelid plasty

In no other area of facial plastic surgery is the balance between form and function as delicate as in eyelid surgery. Given the delicate nature of the structural composition of the eyelids and their vital role in protecting the visual analyzer, iatrogenic interventions in eyelid anatomy must be done carefully, precisely, and with thoughtful consideration of existing soft tissue structures. A brief anatomical review is required to clarify some of the hidden points.

When the eye is at rest, the lower eyelid should be closely attached to the globe, the lid margin should be approximately tangential to the inferior limbus, and the palpebral fissure should slope slightly upward from the medial to the lateral canthus (Western form). The inferior palpebral groove (lower eyelid fold) is usually located approximately 5-6 mm from the ciliary margin and roughly corresponds to the inferior margin of the palpebral cartilage and the transition zone of the pretarsal part of the orbicularis oculi to the preseptal part.

Records

It is believed that the eyelids consist of two plates:

• the outer plate, consisting of skin and the orbicularis oculi muscle,
• the inner plate, which includes cartilage and conjunctiva.

The skin of the lower eyelid, which is less than 1 mm thick, retains its smooth, delicate texture until it extends beyond the lateral orbital rim, where it gradually becomes thicker and rougher. The eyelid skin, which usually lacks a subcutaneous layer, is connected to the underlying orbicularis oculi muscle by thin connective tissue bands in the pretarsal and preseptal areas.

Musculature

The orbicularis oculi muscle can be subdivided into a darker, thicker orbital portion (voluntary) and a lighter, thinner palpebral portion (voluntary and involuntary). The palpebral portion can be further subdivided into preseptal and pretarsal components. The superficial, larger heads of the pretarsal portion unite to form the tendon of the medial canthus, which inserts into the anterior lacrimal crest, while the deep heads unite to insert into the posterior lacrimal crest. Laterally, the fibers thicken and are firmly anchored to the orbital tubercle of Whitnall to become the tendon of the lateral canthus. Although the preseptal portion of the muscle has attachments to the tendons of the lateral and medial canthi, the orbital portion does not; it is inserted subcutaneously into the lateral part of the orbit (participating in the formation of the pes anserinus), covers some of the muscles that raise the upper lip and ala nasi, and is attached to the bone of the inferior margin of the orbit.

Immediately inferior to the muscular fascia running along the posterior surface of the preseptal part of the orbicularis muscle lies the orbital septum. Marking the boundary between the anterior part of the eyelid (the outer plate) and the internal contents of the orbit, it begins at the marginal arc, runs along the orbital margin (a continuation of the orbital periosteum) and merges with the capsulopalpebral fascia posteriorly, approximately 5 mm below the lower edge of the eyelid, it forms a single fascial layer that is fixed at the base of the eyelid.

The capsulopalpebral head of the inferior rectus muscle is a dense fibrous extension which, by virtue of its exclusive attachment to the tarsal plate, produces retraction of the lower lid on downward gaze. Anteriorly it encircles the inferior oblique muscle and, after reunion, thence forwards participates in the formation of the suspensory ligament of Lockwood (the inferior transverse ligament, here called the capsulopalpebral fascia). Although most of its fibres terminate at the inferior orbital margin, some pass through the orbital cellular tissue, participating in its subdivision into spaces, some penetrate the preseptal part of the orbicularis muscle, inserting subcutaneously at the fold of the lower lid, and the remainder pass from the inferior fornix upwards to the Tenon's capsule.

Orbital cellulose

Situated behind the orbital septum, within the orbital cavity, the orbital fat pad is classically segmented into distinct zones (lateral, central, and medial), although in fact there is a connection between them. The lateral fat pad is smaller and more superficial, and the large nasal fat pad is divided by the inferior oblique muscle into a larger central space and an intermediate medial space. (It is important not to damage the inferior oblique muscle during surgery.) The medial fat pad has characteristic differences from the other orbital fat pads, including being lighter in color, more fibrous and dense in structure, and often having a large blood vessel in the middle. The orbital fat pad can be considered a fixed structure, since its volume is not related to the overall body type and does not regenerate after removal.

Innervation

The sensory innervation of the lower eyelid is provided mainly by the infraorbital nerve (V2) and, to a lesser extent, by the infratrochlear (VI) and zygomaticofacial (V2) branches. The blood supply comes from the angular, infraorbital and transverse facial arteries. 2 mm below the ciliary margin, between the orbicularis muscle and the cartilage of the eyelid, there is a marginal arcade that should be avoided when making an incision under the eyelashes.

Terminology

Surgeons in this field must understand a number of descriptive terms commonly used in the eyelid analysis literature.

Blepharochalasis is a commonly misused term. It is a rare disorder of the upper eyelids of unknown origin that affects young and middle-aged women. Blepharochalasis is characterized by recurrent attacks of painless unilateral or bilateral swelling of the eyelids, leading to loss of skin elasticity and atrophic changes.

Dermatochalasis is an acquired condition of increased pathological laxity of the eyelid skin associated with genetic predisposition, natural aging phenomena and environmental influences. It is often associated with orbital fat loss.

Steatoblepharon is characterized by the formation of a true or false herniation of the orbital fat due to weakening of the orbital septum, resulting in areas of focal or diffuse fullness of the eyelids. This condition and dermatochalasis are the two most common reasons for patients to seek surgical help.

A festoon is a single or multiple fold of the orbicularis muscle in the lower eyelid that overhangs one another to create an external hammock-like pouch. Depending on its location, this pouch may be preseptal, orbital, or malar (cheek). It may contain fat.

Malar bags are areas of drooping soft tissue on the lateral margin of the infraorbital ridge and malar eminence, just above the groove between the eyelid and the cheekbone. They are thought to result from symptomatic, recurrent tissue swelling with secondary fibrosis.

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