Use of optical profilometry and visual grading for measurement of longitudinal striations of the nail.

Consumer perception of longitudinal striations of the nail is one of the drivers of nail cosmetic purchase and use. The following work investigates the use of objective instrumental methods for the characterization of longitudinal striations. Striations are quantified by Ra (the average maximum height of the profile), Rq (the root mean square average of the roughness profile), and Rz (the mean roughness depth), industrial roughness parameters, which are calculated using optical profilometry of the three-dimensional surface structure of the nail. A visual assessment is conducted by cosmetologists in vivo and on images captured in several lighting conditions. With this evaluation, the cosmetologists provide ratings of surface ridges on a 0-5 scale to complement and validate the instrumental method. Both the optical profilometry and the cosmetologist-graded methods are used to evaluate 33 nails of visually-varying levels of ridges from female volunteers. The evaluations from these methods yield well-correlated and repeatable results, and these preliminary findings suggest that this new instrumental method can be used to objectively measure longitudinal striations of the nail.