Topography of the skin surface is a mirror of the functional skin status. Surface roughness is an important criterion for assessing the health status of the skin. Changes in roughness occur, among other things, in the case of congenital keratinization disturbances, environment- and job-related skin irritations, infectious skin diseases and age-related defects. Such changes to the skin cannot be objectively evaluated by classical examination methods such as palpation or visual assessment. The biomechanical properties of skin and skin surface contours reflect the structural organization of aging tissues. Therefore, its evaluation is of great interest for dermatological research. As a result, rheological and profilometric measurements permit a simple and noninvasive characterization of the overall aging process of facial skin. Usually, non-invasive methods are used to evaluate the skin surface topography. Most of these methods are based on the preparation of skin replica or reprints. The replica are measured using mechanical or optical profilometry techniques and surface image analysis. Skin contours (the effect of wrinkling on the topography of the skin surface) can be assessed and quantified using optical profilometry and computerized image analysis, although the diversity of measurement methods available with wide variation in experimental conditions has created discrepancies.
Research data showed a significant increase in skin extensibility and a significant decline in elasticity with aging. The loss of tonicity is accompanied by a progressive deepening of facial creases. Age-related rheological alterations was evident with a significant increase in MD (maximum deformation), DD (differential distension), and HY (Hysteresis). Conversely, values of BE (Biological elasticity) declined significantly.
Several skin surface parameters or profilometric variables are used to characterize skin contours -roughness (Ra), depth of roughness (Rz), maximum roughness (Rm, Rz max), waviness (Wt). These parameters indicate different properties of the network of the furrows. The age-related skin contours were measured. The research data show a significant dependence of the skin surface topography on the age the body site measured. Particularly the waviness and the furrow profiles reflect such dependencies. Data obtained from facial samples revealed that Ra showed a non-significant trend in increase over time while Rz increased significantly with age. Rz max or Rm showed by far the greatest relative changes with a value of 42 ± 5 mum in the youngest age and almost doubled every decade. The deepening of natural expression lines was also evidenced by the progressive increase in the number of moderate (150-250 mum) and deep (> 250 mum) furrows, reaching about 15% and 30% per decade, respectively. Significant correlations ( P < .01) were found between values of Rz max and both the decrease in BE and the increase in HY, suggesting the correlation between the changes in biomechanical properties and the skin contours with age.
A disadvantage of the replica technique is that the quality of the skin replica could be compromised such as the formation of air bubbles. Therefore, in vivo methods without direct skin contact may be used for more accurate results. Micro-mirrors is based on the stripe projection onto the skin surface, and measuring its reflection. One such optical system is the PRIMOS optical 3D in vivo skin measurement device.
In order to assess the success of a therapy or of the application of an anti-aging product, the depth, variation and distribution of the furrows and wrinkles need to be measured prior and after application of the pharmaceutical or cosmetic product. The quantification and measurement of skin contours can be used to assess the efficacy of anti-aging anti-wrinkle treatments and procedures such as laser skin rejuvenation techniques by comparing the difference in rheological parameters and skin roughness parameters with that of the skin before applying the treatment.