Functional and Surgical Anatomy of the Eyelids

Alexander J. Altman, MD

Jason Liss, MD

SURFACE ANATOMY

Normal adult eyelids, when open, should form an elliptical fissure that is 8 to 11 mm vertically and 27 to 30 mm horizontally. The lateral canthus is approximately 2 to 4 mm higher than the medial canthus (Figure 2.1).

At rest, the margin of the upper lid will be 1 to 2 mm below the superior limbus.
At rest, the margin of the lower lid will be at approximately the level of the lower limbus. Both upper and lower lids can be divided into anterior and posterior lamellae (Figure 2.2).
Anterior lamella consists of
- Skin
- Orbicularis oculi muscle
Posterior lamella consists of
- Retractors
- Tarsal muscles
- Tarsal plate
- Conjunctiva

SKIN AND SUBCUTANEOUS ANATOMY

The epidermis and dermis of the eyelid

Are the thinnest of the human body (<1 mm)
Lack subcutaneous fat
Demonstrate high flexibility because the eyelid needs to perform rapid movements
These properties limit the sources of graft tissue that can be used for lid reconstructive surgery, with the contralateral upper eyelid often being the best option.

FIGURE 2.1. Eyelid surface anatomy.

FIGURE 2.2. Eyelid cross-sectional anatomy. Anterior lamella includes skin and orbicularis muscle. Posterior lamella includes tarsi, tarsal muscles (Müller and inferior tarsal muscle), conjunctiva, primary retractors (levator muscle and capsulopalpebral fascia).

ORBICULARIS OCULI

The orbicularis oculi muscle, innervated by cranial nerve (CN) VII, is the main protractor of the eyelids. It narrows the palpebral fissure and provides apposition of the eyelids against the globe. This muscle consists of a ring of concentric muscle fibers. It is divided into two contiguous portions (Figure 2.3):

Palpebral
- Divided into pretarsal and preseptal portions; named after the structures they overlie
- Each division arises at the medial canthal tendon from a deep and superficial head. Laterally, these fibers converge to form the lateral canthal tendon, which inserts onto Whitnall’s tubercle, 4 mm posterior to the lateral orbital rim.
- Responsible for involuntary eyelid closure. Medial portions are involved in the lacrimal pump function. Weakness of this apparatus can cause tearing.
Orbital
- Arises from the anterior limb of the medial canthal tendon
- Fibers form a continuous ellipse and insert just below the point of origin at the medial canthal tendon.
- Responsible for forced eyelid closure

PRESEPTAL FAT

Preseptal fat of the upper lid consists of the retro-orbicularis oculi fat (ROOF).
- Lies superficial to the septum but deep to the orbicularis muscle
- Extends superiorly deep to the eyebrow and is adherent to the underside of the orbital portion of the orbicularis muscle
- Contributes to eyebrow volume and motility
- Can descend with aging, causing redundant upper lid skin folds, which can be addressed during cosmetic surgery
  
  FIGURE 2.3. Orbicularis oculi muscle is divided into palpebral and orbital portions.
Preseptal fat of the lower lid consists of the suborbicularis oculi fat (SOOF).
- Nonseptate fat compartment sometimes divided into medial and lateral portions
- Extends inferiorly to the orbitomalar ligament, covering the inferior orbital rim
- Descent with aging leads to “malar bags” and lower eyelid retraction.
- Coupled with orbital fat prolapse, this defect creates the classic double-contour deformity.