49 Botulinum Toxin Injection to Crow’s Feet

Joshua M. Cohen and Sammy Sinno

Abstract

Repeated contraction of numerous facial muscles involved in smiling and squinting, most notably the orbicularis oculi, leads to the formation of canthal lines. These lines initially appear only during animation but over time can become static due to age-related skin changes. Lateral canthal lines, or “crow’s feet,” are one of the FDA approved indications for botulinum toxin.

Botulinum toxin – Botox – canthal lines – crow’s feet – lateral canthus

49 Botulinum Toxin Injection to Crow’s Feet

Key Points

Lateral canthal lines may be due to contraction of the orbicularis oculi during animation. Botulinum toxin injection reduces the orbicularis oculi contraction, thereby reducing the appearance of lines in the lateral canthal region.
The number of botulinum toxin units needed and/or injection points is variable based on the activity of the orbicularis oculi.
A lateral “brow lift” can be achieved by injection of a few units at the tail of the lateral brow.

49.1 Preprocedural Steps

Patients who present for treatment of crow’s feet vary in age, typically starting in their 20s.
Canthal lines have two etiologies:
- Contraction of the orbicularis oculi muscle during animation such as smiling or squinting (Fig. 49.1).
- Excess skin laxity that causes an excess of tissue hanging over the lateral canthal area; these patients commonly have significant wrinkles at rest and will not have significant improvement with botulinum toxin and are candidates for a surgical brow lift.
Asymmetries between the two sides are noted.
It is not uncommon for the eye with more lateral canthal lines or a smaller palpebral aperture to require more neurotoxin.

**Fig. 49.1** Patient demonstrating lateral canthal lines during animation.

49.2 Procedural Steps

See Video 49.1.

49.2.1 Botulinum Toxin Administration to the Crow’s Feet

The patient is prepped with an alcohol swab.
Any large veins in the canthal area are noted and avoided to prevent bruising (Fig. 49.2).
In patients with significant wrinkles in this area, 12 to 15 units of botulinum toxin are used per side.
Three injection points are standard. Treatment starts at the level of the lateral canthus, and then one injection above and one below (Fig. 49.3).
A second “double row” can be injected for a more active orbicularis oculi with peripheral wrinkles.
A lateral “brow lift” can be achieved by injecting an additional 3 to 4 units superiorly just caudal to the tail of the brow (Fig. 49.4).

Fig. 49.2 Standard injection points with anatomical outline and observance of superficial veins.

Fig. 49.3 Standard injection points on patient with visible large superficial vein.

Fig. 49.4 Additional injection point just caudal to the tail of the brow for a “lifting” effect.