Introduction

Patients frequently seek aesthetic rejuvenation of the periocular region. Age-related changes of the bony facial skeleton and soft tissue, in combination with photodamage of the overlying periorbital skin, can lead over time to eyebrow ptosis, drooping of the upper eyelids, and lateral canthal rhytides or ‘crow’s feet’, with a resultant tired or sad appearance. In fact, the periocular region is often a candid indicator of someone’s age, with crow’s feet developing early on in the aging process, often by the 3rd and 4th decades of life. The eyes serve as an integral component of facial recognition and have been considered a marker for physical attractiveness and beauty. During non-verbal communication, subtle differences in eyebrow and eyelid contour and position convey a broad range of emotions, from surprise, to fear, and happiness. By integrating the concepts of facial symmetry, sexual dimorphism, and ethnic diversity, along with a global understanding of the anatomy and aesthetics of the periocular region, the clinician can achieve successful facial rejuvenation. The overall result may emerge from a comprehensive treatment algorithm, including topical skin care, botulinum toxin injection, soft tissue augmentation, skin tightening, and cutaneous rejuvenation and resurfacing. In this chapter, we will focus on the indications and treatment guidelines for botulinum toxin in the periocular region.

Anatomy of ‘crow’s feet’ lateral orbital rhytides

A thorough understanding of the functional anatomy of the periocular region must precede treatment. Eyelid skin is elastic and among the thinnest of the body, with essentially no underlying subcutaneous fat. Crow’s feet are fine or coarse rhytides originating from the lateral ocular canthus and projecting outward, often in a partial or full fan-like distribution. Most prominent during the so-called ‘dynamic’ states of smiling or squinting, crow’s feet can be appreciated in repose, the ‘static’ posture, in certain patients. Several factors contribute to the development of crow’s feet, including sun exposure, smoking, lack of subcutaneous fat, and redundant skin.

In addition, rhytides develop in the setting of hyperkinetic muscle contractions of the orbicularis oculi, an elliptical muscle that functions in closing the eyelids and protecting the globe by acting as the sphincter of the eye. The orbicularis oculi encircles the eye, with a predominantly vertical orientation at the lateral canthus, and has three distinct subparts: the orbital, palpebral, and lacrimal portions. The lacrimal portion of the muscle runs deep to the lacrimal sac and inserts on the upper and lower eyelids at the tarsal plates. Contraction of this part of the muscle draws the eyelids against the globe and compresses the lacrimal sac, thus assisting tear flow. The palpebral portion is the innermost aspect of the muscle and passes into the eyelid superficial to the septum from the bifurcation of the medial palpebral ligament to the lateral palpebral raphe. The palpebral portion is subdivided into preseptal and pretarsal components, and each portion is superficial to the corresponding named portion of the eyelid. Contraction of the palpebral portion of the orbicularis oculi provides less forceful involuntary closure of the eyelid, as with blinking. The orbital portion represents the outermost aspect of the muscle overlying the bony orbit, with origins at the nasal process of the frontal bone, frontal process of the maxilla, and the medial palpebral ligament. This portion of the muscle blends into surrounding musculature, interdigitating at its superior aspect with the frontalis muscle, corrugator supercilii, depressor supercilii, and procerus muscles, and at its inferior margins with the levator labii superioris alaeque nasi, levator labii superioris, and zygomaticus minor and major muscles (Fig. 15.1). By providing forceful eye closure and eyebrow depression, this outer aspect of the muscle pulls on overlying skin and contributes most to the formation of lateral orbital rhytides. The outer orbicularis is typically treated with botulinum toxin, although the preseptal aspect of the inferior palpebral portion of the orbicularis oculi can be treated in some situations as well. The zygomaticus muscles, both major and minor, can also contribute to inferior periorbital rhytides, as contraction of this muscle elevates skin superiorly into the periocular region. The zygomaticus major originates deep to the orbicularis oculi muscle at the zygomatic bone just anterior to the zygomaticotemporal suture line and courses diagonally where it inserts into the modiolus, lifting the corner of the mouth. The zygomaticus minor muscle courses from the zygomatic bone and inserts into the upper lip, where it causes upward and lateral elevation of the oral commissure. The risorius muscle originates from the connective tissue and fascia overlying the parotid gland, platysma, and runs horizontally towards the oral commissure, where it inserts into the modiolus. Contraction of this muscle pulls the mouth laterally, retracting the corners of the mouth.

Figure 15.1 The muscles of facial expression.

In an article by Kane et al, four lateral canthal rhytid patterns were identified, reflecting divergent muscle contraction patterns: (1) full-fan distribution of rhytides from the upper eyelid to the upper cheek, (2) rhytides of the lower lid / upper cheek, (3) rhytides of the upper eyelid skin down to the lateral canthus, and (4) central zone of rhytides at the lateral canthus only (Fig. 15.2). Although standard injection points can be helpful for beginner injectors, treatment should be individualized to take into account this diversity in lateral canthal rhytides, which may deviate from published patterns and require care and attention to understand, document, and address specifically. Some patients may exhibit right–left differences in the distribution and size of lateral canthal rhytides. Lateral canthal rhytides are generally classified as static, dynamic, or a combination of the two. Dynamic rhytides develop secondary to repeated muscle contractions, and remit during relaxation, and hence are most immediately amenable to treatment with botulinum toxin. Static rhytides, which are present in the absence of muscle contractions, may best be treated with soft tissue fillers or resurfacing procedures, and will be addressed later in this chapter. Alternatively, ongoing and repeated treatments with botulinum toxin may soften static rhytides over long time intervals, as reduction of coincident dynamic creases reduces the incidence of repeated microtrauma to the underlying collagen and elastin. Botulinum toxin treatments may also prevent the extension or deepening of static creases through a similar mechanism.