Development and validation of a standardized photonumeric crow’s feet grading scale: the Korean-Adapted Crow’s Feet Grading Scale

Background Objective, validated photonumeric grading scales tailored to East Asian facial anatomy are essential for aesthetic clinical trials. We developed and validated the Korean-Adapted Crow’s Feet Grading Scale (K-CFGS), a 5-point photonumeric tool for assessing static lateral canthal lines in East Asian skin.Methods This clinical validation study enrolled 75 Korean participants aged 19 to 65 years. Standardized two-dimensional digital photographs were obtained with head positioning aligned to the Frankfort horizontal plane and lighting controlled. Three independent expert evaluators performed blinded photographic ratings in two sessions separated by a 3- to 4-week washout period. Standardized visual references were supplemented with detailed Korean-language criteria to improve evaluation accuracy. Under the principal investigator’s supervision, images from 50 participants were selected for the final validation analysis, with 10 participants per grade (grades 0–4).Results All three evaluators demonstrated high intrarater repeatability (weighted κ=0.815–0.860). Inter-rater agreement increased from substantial in round 1 (Fleiss κ=0.603) to almost perfect in round 2 (Fleiss κ=0.825). Blinded evaluator ratings correlated very strongly with live investigator assessments (Spearman rs=0.887) and strongly with patient self-evaluations (Spearman rs=0.764); both correlations were positive.Conclusions The K-CFGS provides a reproducible, objective primary endpoint matched to East Asian populations for clinical trials of periorbital tissue restoration, soft-tissue fillers, and aesthetic medical devices.