Slight alterations in the intricate anatomy of the upper and lower eyelid or their underlying structures can have pronounced consequences for ocular esthetics and function. The understanding of periorbital structures and their interrelationships continues to evolve and requires consideration when performing complex eyelid interventions. Maintaining a detailed appreciation of this region is critical to successful cosmetic or reconstructive surgery. This article presents a current review of the anatomy of the upper and lower eyelid with a focus on surgical implications.
Key points
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The complex anatomy of the upper and lower eyelid and its interrelation with underlying structures has important consequences for both esthetics and function.
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A strict understanding of the anatomic relationships of the eyelid components will help the facial plastic surgeon approach eyelid surgery safely and effectively.
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The structures of the upper and lower lid have many contiguous structures but several key differences that are important to recognize when performing periorbital procedures.
Introduction
The surgical anatomy of the eyelid is one of the most complex in the head and neck, and a thorough understanding of the intricacies is paramount for facial plastic surgeons. The eyelid functions to provide lubrication to the cornea while also serving as a barrier to foreign bodies. Lubrication of the corneal surface is achieved by a protective tear film, which is spread over the surface by periodic blinking. A multilayered tear film is formed from the lacrimal gland as well as small glands in the eyelid. The combination of mucus, oil, and aqueous materials provides a lubricating film that is eventually broken down by the atmosphere. Periodic blinking helps to replenish the balance of this important tear film.
The normal adult eyelids form an elliptical palpebral fissure measuring 8 to 11 mm vertically at the pupillary meridian by 27 to 30 mm horizontally. There are subtle but important differences when evaluating the upper and lower eyelid. The upper lid rests 1 to 2 mm below the superior limbus of the iris, while the lower lid rests along the inferior limbus. The lateral canthus is 2 to 4 mm higher than the medial canthus, and the interpalpebral distance is 10 to 12 mm ( Fig. 1 ).
The upper and lower eyelids are composed of several analogous structures. Most commonly, these structures can be divided into an anterior, middle, and posterior lamellae. The anterior lamella refers to the skin and orbicularis oculi muscle of the eyelid. The posterior lamella refers to the retractors, superior or inferior tarsal muscle, tarsus, and the conjunctiva. Some investigators also reference the orbital septum as the middle lamella; however, this can vary depending on the source. The through-and-through layers are different depending on one’s vertical position over the eyelid and are discussed in the following sections ( Fig. 2 ).
Introduction
The surgical anatomy of the eyelid is one of the most complex in the head and neck, and a thorough understanding of the intricacies is paramount for facial plastic surgeons. The eyelid functions to provide lubrication to the cornea while also serving as a barrier to foreign bodies. Lubrication of the corneal surface is achieved by a protective tear film, which is spread over the surface by periodic blinking. A multilayered tear film is formed from the lacrimal gland as well as small glands in the eyelid. The combination of mucus, oil, and aqueous materials provides a lubricating film that is eventually broken down by the atmosphere. Periodic blinking helps to replenish the balance of this important tear film.
The normal adult eyelids form an elliptical palpebral fissure measuring 8 to 11 mm vertically at the pupillary meridian by 27 to 30 mm horizontally. There are subtle but important differences when evaluating the upper and lower eyelid. The upper lid rests 1 to 2 mm below the superior limbus of the iris, while the lower lid rests along the inferior limbus. The lateral canthus is 2 to 4 mm higher than the medial canthus, and the interpalpebral distance is 10 to 12 mm ( Fig. 1 ).
The upper and lower eyelids are composed of several analogous structures. Most commonly, these structures can be divided into an anterior, middle, and posterior lamellae. The anterior lamella refers to the skin and orbicularis oculi muscle of the eyelid. The posterior lamella refers to the retractors, superior or inferior tarsal muscle, tarsus, and the conjunctiva. Some investigators also reference the orbital septum as the middle lamella; however, this can vary depending on the source. The through-and-through layers are different depending on one’s vertical position over the eyelid and are discussed in the following sections ( Fig. 2 ).
Anterior lamellae
Upper Eyelid
The skin is the most superficial layer of the upper eyelid and is unique in that it is the thinnest skin of the body. The necessity for rapid eyelid movements during blinking requires the skin to be highly flexible. Because of this intrinsic quality, there are very few adnexal structures or sebaceous glands in this skin. From a reconstruction standpoint, this often poses a challenge, as the reconstructive dictum of “replacing like with like” limits options to using the contralateral eyelid skin as the ideal source. Other skin graft donor sites can be too thick and may become cosmetically unacceptable.
Just below the skin of the upper eyelid lies the orbicularis oculi ( Fig. 3 ). The orbicularis oculi is divided into orbital and palpebral portions. The orbital portion is formed by concentric muscle fibers arising from the medial canthal tendon, and it functions to close the eyes tightly. Laterally, the fibers insert subcutaneously and contribute to the formation of “crow’s feet.” The palpebral portion consists of semilunar muscle fibers that span the medial and lateral canthal tendons. It can be further subdivided into pretarsal and preseptal portions, named by the structures they overlie. Medially, each subdivision arises from 2 heads, with the superficial heads arising from the insertion of the medial canthal tendon onto the anterior lacrimal crest, while the deep heads insert near the posterior lacrimal crest. The medial portions of the palpebral orbicularis help with the lacrimal apparatus. Laterally, the fibers condense to form the lateral canthal tendon, which inserts onto Whitnall tubercle, located approximately 4 mm posterior to the lateral orbital rim.
Lower Eyelid
The lower eyelid anterior lamellae structures of skin and orbicularis muscle are analogous to the upper eyelid (see Fig. 2 ).
Orbital septum and preseptal fat pads
Upper Eyelid
The orbital septum is a critical structure of the upper eyelid, separating the orbital contents into preseptal and postseptal compartments. The orbital septum is a multilaminar fibrous sheet originating from the arcus marginalis, a fibrous line derived from the periosteum of the superior orbital rim. The septum fuses with the anterior layer of the levator aponeurosis 2 to 3 mm above the tarsus. Variance in this attachment is noted and can extend from 0 to 10 mm from the superior tarsal edge. In the Asian eyelid, this fusion point can be absent or very low, resulting in the so-called single eyelid. As the septum weakens with age, the postseptal fat begins to prolapse anteriorly and pseudoherniate, creating a visible bulge. These changes are important to consider when correcting the upper eyelid esthetic.
Superficial to the orbital septum, but deep to the orbicularis muscle is the adipose tissue commonly referred to as the retroorbicularis oculi fat (ROOF). This fat runs beneath the ciliary portion of the eyebrow and connects under the orbital portion of the orbicularis oculi muscle. The ROOF contributes to eyebrow volume and mobility of the lateral eyebrow and eyelid.
Lower Eyelid
In the lower lid, the septum fuses with the capsulopalpebral fascia (analogous to the levator aponeurosis in the upper lid) about 5 mm inferior to the tarsus. However, in the Asian eyelid, this fusion may be nonexistent or much closer to the tarsus.
Just deep to the orbicularis in the lower lid lies the suborbicularis oculi fat pad (SOOF), analogous to the ROOF in the upper lid. These fat pads are distinct from the orbital fat pads, which are posterior to the orbital septum. The SOOF continues inferiorly below the orbitomalar ligament, where it pads the inferior orbital rim. Ptosis of the SOOF can lead to “malar bags” and contour deformities because the inferior orbital rim becomes exposed. Ptosis of the SOOF, in conjunction with prolapse of orbital fat, can create the classic double-contour deformity.
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