SWIRL, a clinically validated, objective, and quantitative method for facial wrinkle assessment.

Background: Facial wrinkles are an undesirable feature caused by extrinsic photodamage and intrinsic aging process. Many cosmetic products and esthetic procedures strive to ameliorate the appearance of wrinkles. Currently the effects of those products and procedures on wrinkles are mainly evaluated by clinical grading, subjective self-assessment questionnaires, and optical profilometry of replica impressions. An objective and quantitative method is in demand.

Methods: Raking light optical profilometry was applied directly to facial photography to cast wrinkles as dark shadows. The resulting high-resolution digital images were analyzed using Image Pro software. A high-throughput method, Stephens Wrinkle Imaging using Raking Light (SWIRL), was developed to analyze the severity of wrinkles using photographs taken under the raking light condition. This method was applied to photographs taken from many panelists with a wide range of wrinkle severity scores. The result was compared with clinical grading scores to determine its validity. In addition, this method was applied to photographs taken from panelists before and after product usage to determine its sensitivity.

Results: Using the SWIRL method, multiple wrinkle parameters were quantitatively assessed, including wrinkle count, length, width, area, and relative depth. Those parameters correlated well with clinical grading scores, showing correlation coefficient (r value) of about 0.8 for all parameters. This result indicates that the SWIRL method is a valid method for analyzing wrinkle severity. When applied to a clinical study, the SWIRL method was sensitive enough to detect improvement after 8 weeks of product application.

Conclusions: The SWIRL method has been fully validated through clinical studies. It is accurate, objective, and quantitative. As multiple wrinkle parameters are analyzed simultaneously, it can provide more detailed information on how wrinkles change over time and therefore has the potential to shed light on the action and mechanism of antiwrinkle products.