A thorough understanding of the periorbital anatomy is necessary to achieve optimal aesthetic surgical results while avoiding potential complications.

The eyelids and surrounding structures can be divided into five anatomical zones (FIG 1).^1,2 Zone I and zone II represent the upper and lower eyelid, respectively. Zone III represents the medial canthus and lacrimal drainage system. Zone IV includes the lateral canthal region and lateral retinaculum. Zone V represents the surrounding periorbital structures and includes the forehead, brow, glabellar, temple, malar, and nasal regions.

Lower eyelid procedures including lower eyelid blepharoplasty and lateral canthopexy or canthoplasty focus on zones II and IV. The lower eyelid or zone II can be thought of as a trilamellar structure that consists of an anterior, middle, and posterior lamella. The anterior lamella consists of skin and orbicularis oculi muscle that is further divided into pretarsal, preseptal, and orbital components. The pretarsal and preseptal components are often referred to as palpebral portions. The middle lamella includes the tarsus, orbital septum, and retroseptal fat, while the posterior lamella denotes the capsulopalpebral fascia and conjunctiva.

The tarsal plate of the lower eyelid on average measures 25 mm wide, 4 mm in height, and 1 mm in thickness and provides structural integrity to the eyelid.

The lateral canthus or lateral retinaculum (zone IV) is a three-dimensional fibrous structure that connects the upper and lower tarsal plates to the Whitnall tubercle, located 8 mm posterior to the lateral orbital rim (FIG 2). These structures converge at the lateral canthal angle, typically approximately 1.5 to 2.0 mm above the medial canthal angle. This aesthetically pleasing and favorable relationship of the lateral canthus above the medial canthus is often referred to as a positive canthal tilt. When the lateral canthus is at the level of or below the medial canthus, this is referred to as neutral or negative canthal tilt, respectively. It is the lower eyelid portion of the lateral retinaculum or the “inferior retinaculum” that is the focus of the lateral canthopexy or canthoplasty techniques that will be described in this chapter.

Despite distinct ethnic and cultural differences, the youthful eye resembles an almond shape, which has a long and narrow palpebral fissure and an upward inclination of approximately four degrees laterally. In patients with loss of lateral canthal support, the lateral palpebral fissure takes on a more rounded appearance with concomitant laxity of the lower eyelid margin. The pathophysiology of lateral canthal disorders is attributed to the loss of canthal support from gravitational, mechanical, or involutional factors.

A subset of patients are at increased risk for lower eyelid malposition resulting from lower blepharoplasty. In such patients, lateral canthal tightening may be indicated to help prevent these sequelae.

The preoperative assessment begins with a detailed medical history with emphasis on risk factors that may lead to postoperative complications. A past medical history of hypertension, diabetes, thyroid disease, bleeding diathesis, glaucoma, dry eyes, trauma, and periorbital and facial operations, including refractive surgery, is of particular significance and should be documented. Furthermore, the use of medications that include nonsteroidal anti-inflammatory, anticoagulants, and aspirin should be recorded and held for a minimum of 2 weeks prior to surgery.

The physical exam should be performed with the patient sitting in an upright, relaxed position and should begin with an assessment of visual acuity, pupillary reflexes, extraocular muscle movement, and an intact Bell phenomenon.³ A focused lower eyelid exam should document the presence of malar bags, fat herniation, dermatochalasis, tear trough deformities, and skin pigmentation. In addition, the senior authors have previously identified seven key features that should be assessed in patients undergoing lower eyelid procedures and include the following: canthal tilt, vector analysis, scleral show, tarsoligamentous integrity, lateral canthal-orbital rim distance, midface position, and vertical restriction.² This standard preoperative checklist is provided in FIG 3.

Canthal tilt assesses the relationship of the medial and lateral canthus (FIG 4). The average position of the lateral canthus is approximately 1.5 to 2 mm cephalad to the medial canthus thus resulting in a positive tilt. Canthal tilt can be described as positive, negative, or neutral.