Treatment of crow’s feet

Introduction

Patients often desire 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. Indeed, the periocular region is often a candid indicator of an individual’s age, with crow’s feet developing early on in the aging process, often by the third and fourth decades of life. The eyes serve as an integral component of facial recognition and have been considered a marker for physical attractiveness and beauty. 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 in 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 at rest, the “static” posture, in certain patients. Many 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 muscle is a broad muscle composed of concentric striated fibers that encircle the orbital rim with a predominantly vertical orientation at the lateral canthus. The orbicularis oculi has three distinct subparts: the pretarsal, preseptal, and orbital portions are the major components. The lacrimal is a small offshoot but not a main component of the muscle. The lacrimal portion of the muscle runs deep into 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 with tear flow. The preseptal orbicularis oculi muscle divides medially into a deep head and a superficial head. The deep head of the muscle attaches to the fascia around the lacrimal sac as well as the posterior lacrimal crest, while the superficial head of the muscle attaches to the anterior limb of the medial canthal ligament. Laterally, the preseptal orbicularis oculi muscle attaches to Whitnall lateral orbital tubercle, which is deep to the lateral palpebral raphe.

The pretarsal orbicularis oculi muscle also divides medially into a deep head and a superficial head. The deep head of the muscle attaches behind the posterior lacrimal crest and to the medial canthal tendon, while the superficial head of the muscle attaches to the anterior lacrimal crest. The deep or posterior head of the pretarsal orbicularis oculi muscle is also known as Horner’s muscle. Laterally, the muscle attaches to the lateral canthal tendon. The superior and inferior pretarsal orbicularis oculi muscles are overlain by the respective upper and lower eyelid tarsi. The muscle is firmly adherent to the underlying tarsus.

The pretarsal and preseptal portions are the innermost components and pass into the eyelid superficial to the septum from the bifurcation of the medial palpebral ligament to the lateral palpebral raphe. Contraction of these portions 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, the 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. 18.1 ). By providing forceful eye closure and eyebrow depression, this outer aspect of the muscle pulls on the 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 orbicularis oculi can also be treated in some situations.

The orbicularis muscle can contribute to crow’s feet lines (CFLs). However, not all crow’s feet lines are caused by the orbicularis muscle alone. Rhytides that occur with smiling do represent activity of the zygomaticus; rhytides that occur when patients force their eyes shut as if someone were about to splash water on them occur as a result of orbicularis contraction. It is important to note that the rhytides identified as “crow’s feet” that are actually due to contraction of the zygomaticus must not be treated with neuromodulators. The zygomaticus muscles, both major and minor, can also contribute to inferior periorbital rhytides because contraction of this muscle elevates the 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.

Kane et al. describe four lateral canthal rhytid patterns that reflect the 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. 18.2 ). Although standard injection points can be helpful for beginner injectors, treatment should be individualized to take into account this diversity in lateral canthal rhytides. 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 because 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.