This article discusses the anatomy of the periocular region in terms of how the parts interact and what happens anatomically with aging. Detailed function of the anatomic area is also presented. Periocular anatomy, the lacrimal system, and orbital anatomy are first discussed, followed by characteristics of aging.
Eyelid anatomy is one of the more complex sets of anatomic relationships in the face. Differences are measured in millimeters, and structures are extremely fine and delicate ( Fig. 1 ). The tissue can be very difficult to work with, requiring the utmost attention to detail. It is imperative to have an understanding of the complex anatomy and function of this region before any surgical or nonsurgical adventure is undertaken.
Anatomic descriptions involve western aesthetic tenets in Caucasians unless otherwise specified; although, as there are ever-increasing variations in aesthetic goals and many varying ethnicities, there is some generalization. The function of the lacrimal system and the orbital contents are beyond the scope of this article and are addressed only as they pertain to nonophthalmologic procedures.
A few anatomic relationships are important when evaluating the orbital region. First, brow position may be evaluated. Common aesthetic relationships differ. In men, the brow is often most pleasing at the superior orbital rim in a less arched position. In women, the brow is ideally described as club-shaped, beginning in line with the alar creases medially at the orbital rim and arching above the rim with the apex over the lateral limbus and descending back down to the level of the orbital rim.
The upper lid crease is formed by the insertion of the levator aponeurotic fibers into the skin ( Fig. 2 ). The crease is usually 8 to 9 mm in men and 9 to 12 mm in women. In the Asian population, the insertion is significantly closer to the lid margin, resulting in a lower or absent crease. The lower lid fold may be 3 mm from the lid margin and is more common in the pediatric population ( Fig. 3 ).
The palpebral fissure is 28 to 30 mm wide and 9 to 10 mm high, with the lateral canthal angle 2 mm higher on a horizontal plane than the medial canthus (3 mm in the Asian population). The lateral canthal angle is 30° to 40°. The medial canthus lies about 15 mm from the midline (see Fig. 3 ).
The upper lid margin lies from the level of the superior limbus to 2 mm below normally. Upper lid excursion may average 12 mm, whereas lower lid excursion is 5 mm.
The eyelids are constructed with 3 anatomic and surgical layers: anterior, middle, and posterior lamellae ( Figs. 4 and 5 ). The anterior lamella is composed of the skin, subcutaneous tissue, and orbicularis muscle. The skin is often less than 1 mm thick and may be thin enough to reveal underlying vessels and discoloration. Beneath the skin, there is some loose connective tissue in the preseptal and preorbital regions, which is absent in the pretarsal area. This subcutaneous tissue allows for the easy separation of the skin and muscle during surgical dissection.