Comparison of two in vivo measurements for skin surface topography

Background/purpose Non-contact methods for quantifying skin surface topography in vivo are common in skin research. The surface evaluation of living skin (SELS) and the phaseshift rapid in vivo measurement of skin (PRIMOS) are two approaches to measure skin surface roughness and wrinkling via optical methods. The aim of this study was to compare the reliability and interrelatedness of the parameters obtained by both technologies. Methods Three repeated measurements were conducted on four skin areas (from distal to proximal) on the volar forearm skin in 12 healthy young subjects with two different instruments using the SELS and PRIMOS methods. Subjects mean age was 32.9 (SD 7.2)years. Skin phototypes were II (n=7), III (n=4), and IV (n=1). The SELS parameters, smoothness (SEsm), roughness (SEr), scaliness (SEsc), and wrinkles (SEw), and a range of DIN/ISO surface roughness parameters were obtained. Intraclass correlation coefficients to estimate the reliabilities and correlation coefficients for estimating strengths and directions of relationships were applied. Results Values of obtained parameters were very well comparable across the four skin areas. Reliability of the four SELS parameters was very high ranging between 0.95 and 1.00. Reliability coefficients for the roughness parameters varied between 0.35 and 1.00, whereas half of all PRIMOS estimates showed measurement errors less than 20%. SELS and the PRIMOS roughness parameters were largely unrelated. Conclusion Both measurement technologies provide reliable estimates indicating that skin surface measures of the volar forearm in young adults can differentiate between skin areas of different persons or different treatments in clinical studies. Skin surface topography of the volar forearm is comparable from distal to proximal assuring baseline comparability after randomization in clinical trials. SELS and PRIMOS roughness parameters of the volar forearm are not comparable and contain different types of information.