One of the most common complaints of aging patients is the appearance of crow's feet lines in the lateral canthal region. Many different treatment methods, including chemical peels, surgical procedures, filler material injections, botulinum toxin injections, and laser resurfacing, have been used for effacement of these lines among aging patients and patients with sun damage. Despite the fact that many scientific articles have been written regarding the treatment of crow's feet lines, the actual patterns of these lines have not been adequately studied or classified. Several different patterns of animation in this area have been observed. These different patterns and their frequencies are described. All crow's feet patterns are not the same, and it follows that treatment of different patterns of crow's feet lines should be adapted to the particular patterns.
One of the areas in the upper face that is most frequently considered for rejuvenative treatment is the crow's feet area. Crow's feet are the lines that radiate outward from the lateral canthus during smiling. Histological examination of crow's feet reveals a configurational change in the skin attributable to deterioration of the elastic tissue network. 1 With full animation, these lines are apparent even among some teenagers. By their late thirties, most patients exhibit the lines even in repose. The amount and depth of crow's feet lines differ among patients. Among the key variables are prior sun damage, 2 skin thickness, 2 amount of subcutaneous fat, smoking history, 3 and amount of contraction of the lateral orbicularis oculi muscle during smiling or squinting. 4 Compared with skin with less sun exposure (postauricular skin), crow's feet skin demonstrates reduced epidermal thickness, a more compact stratum corneum, increased granular layer thickness, increased perifollicular fibrosis, and increased solar elastosis. 2 Some individuals forcibly contract this muscle even when smiling only slightly, and others slightly wrinkle the area when smiling strongly.
Many treatments for crow's feet lines have been described. Chemical peels have long been used to improve fine rhytids in this area. 5-7 Surgical procedures 8 that weaken the orbicularis oculi muscle, 4,9 thus decreasing wrinkling of the fine skin above the muscle, have also been described. Injectable collagen has been used to fill these fine rhytids for more than 20 years. 10-12 I have used botulinum toxin type A to efface these fine rhytids since 1991. The use of botulinum toxin for cosmetic purposes was first described in the medical literature in 1992. 13 The ability of the toxin to alleviate crow's feet lines was first described in the literature in 1993. 14 Since that time, many other reports have validated the use of the toxin for treatment of various dynamic rhytids of the face. 15-20 Before the explosive growth in the use of the toxin for cosmetic procedures, its use for the treatment of medical conditions was well established. 21-28 A few years later, laser resurfacing was added to the methods used for improvement of crow's feet lines. 29,30 Surgical procedures, 31 including brow lifts, 32,33 that do not weaken the lateral canthal musculature have also been used to diminish lines in this area. Topical application of retinoids 34,35 and ascorbic acid 36 has also proved beneficial. Subdermal wounding of the skin in this area of the face has produced increased collagen levels and skin contraction. 37 Dermabrasion is not frequently performed, because of the thinness of this fine skin.
Although many procedures have been reported for the treatment of crow's feet lines and the histological features have been described, the area itself has not been thoroughly described. When treatment is discussed, it is usually with a one-size-fits-all approach. In most articles, crow's feet lines are assumed to be basically the same among individuals, with some differences in the depth of the lines resulting from age, hereditary factors, or environmental factors; however, this is not the case. I first became aware of the differences when I began to photograph patients treated with botulinum toxin type A. I noticed wide variation in the patterns that the patients exhibited during animation. I observed that the crow's feet lines could be grouped into certain identifiable patterns, which were analogous to the smile patterns described by Rubin 38 in 1974. I did not arbitrarily create patterns and then try to fit patients into those patterns. These were simple patterns that I observed during many years of injecting crow's feet lines with botulinum toxin. Just as people tend to exhibit different smile patterns, they also exhibit different crow's feet patterns. This should be kept in mind when this area is treated with any method, but I have found it especially important for treatment of the area with botulinum toxin.