LONGITUDINAL STRIATIONS OF THE NAIL 95 acceptable. Nails were required to be bare and absent of any products that could interfere with the fringe projection measurement. Because of the nail’s capacity to become en- gorged when hydrated, it was important to allow the nails to acclimate for a recom- mended 30 min at 21°C ± 1°C and 45% ± 5% relative humidity after washing to ensure that hydration effects did not distort the surface nail shape (8). OPTICAL PROFILOMETRY FRINGE PROJECTION METHOD Optical profi lometry fringe projection has been used previously in surface structure mea- surements for wrinkles in the skin (9) and for nail surface irregularities (10). Fringe pro- jection works by projecting various patterned bands of light onto the object surface, recording the image, and reconstructing the surface shape based on the distortions of the pattern. This noninvasive method provides a 3D model of the measured surface, which can then be used to determine a number of dimensions of the sample. Provided the sample is suffi ciently stationary for the duration of the measurement, fringe projection can be used on in vivo samples. The GFM PRIMOS Pico #108-000136 (GFM, Tetlow, Germany) was used to capture the individual nail 3D models. Volunteers were instructed to place the fi nger in the stereo- tactic fi nger-positioning device that avoided motion impact on the capture. This ensured that all samples were measured at the same distance from the camera (14.5 cm) and that the fi eld of view was 45 × 40 mm. All measurements were thus comparable. The GFM PRIMOS Pico projected a series of lateral bands onto the nail in quick succession and constructed the 3D model with its associated software. Analysis of the 3D models utilized the instrument’s associated software to process each nail model to obtain three industrial roughness parameters: (i) Ra, or the average maxi- mum height of the profi le, (ii) Rq, or the root mean square average of the roughness profi le, and (iii) Rz, or the mean roughness depth. A few post processing steps were taken to ensure that the parameter only measured the desired striations and was not affected by the lateral and proximal folds intersecting the nail, the curved nature of the nail, or the proximal-to-distal variability of the nail. Specifi cally, the model was cropped to only in- clude the fi ngernail region. A polynomial fi lter (of order n = 3) was applied to remove the transversal and longitudinal curvature of the nail. Finally, a low-pass averaging fi lter (15 pixels distal to proximal, 3 pixels transversal) was applied to reduce the impact of proximal- to-distal variability of the striations on the nail. The Ra, Rq, and Rz measurements were acquired by averaging the respective values measured across fi ve equidistant and parallel transverse cross-sections. COSMETOLOGIST ASSESSMENT METHOD A group of three trained cosmetologists proceeded to grade together the severity of lon- gitudinal ridges seen for a given nail on an 11-point scale at a 0.5-level interval. A value of 0 indicated no ridges and a value of 5 indicated the most severe ridges. The term “ridges” was used in place of striations as it is more common in the cosmetologist ver- nacular and more easily understood. The cosmetologist assessment included the assess- ment of both surface and underface aspects of longitudinal striations, though an emphasis was placed on the severity, number, and depth of the furrows on the surface of the nail.

JOURNAL OF COSMETIC SCIENCE 96 Training of the cosmetologists was conducted using a photo atlas (i.e., Figure 1). Cosme- tologists were trained together, and an effort was made to harmonize them on a number of volunteer subjects. Just as with standard clinical evaluation tools, use of a valid typo- logical atlas can increase precision of cosmetologist grading by reducing variability be- cause it serves as a tangible and visual frame of reference for experts. These assessment scores provide the best available standard as there is no existing standardized method for measuring ridges. In addition to the in vivo assessment, cosmetologists evaluated the longitudinal ridge severity of these nails from images captured in several lighting modalities. Cosmetologists graded the nails in vivo immediately before the optical profi lometry capture, and then graded nails—shown in random order—of three image types: a set captured in parallel- polarized (PPOL) lighting, a set captured in cross-polarized (XPOL) lighting, and a set captured by the PRIMOS at the time of the 3D optical profi lometry capture. PPOL and XPOL images for cosmetologist assessment were captured using a Nikon D90 DSLR camera (Nikon Corporation, Tokyo, Japan), polarizing fi lters on the off-body fl ash devices and camera lens, and consistent instrument positioning. The use of PPOL light is generally considered best for capturing the surface relief of an object and therefore is appropriate for illustrating the severity of ridges in Figure 1. Similar to the capture of the optical profi lom- etry fringe projection image, a stereotactic device was utilized to maintain standardized positioning of the fi ngers for PPOL and XPOL imaging for cosmetologist assessment. ANALYSIS The measurement procedure to obtain Ra was repeated three times for each nail. These triplicate measurements were used to examine the repeatability of the method. Specifi - cally, the image processing step was repeated three times from start to fi nish for each nail, using the same 3D image. Because the stereotactic device ensured positioning consis- tency throughout image capture, image analysis was not repeated using different images. Several regressions were run between the optical profi lometry roughness parameters with the various cosmetologist assessments of ridges to determine how correlated the methods were. Because the fringe projection method solely measured the surface striations while the cosmetologist assessments involved the evaluation of both surface and underface stri- ations, there was a possibility for an innate difference between the methods and for them to not be well correlated. A Pearson correlation coeffi cient (r) of 0.60–0.79 was accepted as indicative of a strong correlation (11). Figure 1. Cosmetologist scale of longitudinal ridges, where a value of 0 indicates no ridges and a value of 5 indicates the greatest severity of ridges. Ridges are graded at a 0.5-level interval. Images for the scale are captured in a PPOL lighting modality.