title: A novel method to investigate the relationship between facial movements and wrinkle formation using particle image velocimetry.
abstract: BACKGROUND
  The possible relationship between the direction of wrinkles and the movement of facial skin has not previously been reported. Therefore, we characterized that relationship using particle image velocimetry (PIV) analysis.
  
  
  METHODS
  Twenty-one healthy Japanese women aged in their 20s (n = 7) or 50s (n = 14) were recruited for this study. Moving images of facial skin motions (closing the eyes tightly, raising the eyebrows) were captured using a single infrared camera under infrared ray irradiation of the skin. PIV analysis was then carried out using Flow-Vec32 software to determine the velocity and the direction of skin surface movements.
  
  
  RESULTS
  All skin movements caused by those motions were finished within 0.20 s. During the motion of closing the eyes, skin at the eye periphery did not move in a superior-inferior direction, but did move toward the center of the eye (pupilla) with complex flows. There was no significant difference between either age group of subjects. During the motion of raising the eyebrows, the forehead skin moved upwards (direction to parietal) with relatively uniform flows. The velocity of movement at the top was lower than at the bottom, and that difference is likely to cause a deformation on the skin surface. A significant difference between the two age groups in the velocity was observed.
  
  
  CONCLUSIONS
  The results show that the deformation of older skin on the forehead is greater than that in younger skin. The PIV analysis method is a useful tool to investigate some aspects of the relationship between facial skin movements and wrinkle formation.
authors.affiliation: Kao Corporation, Biological Science Laboratories, Tochigi, Japan. fujimura.tsutomu@kao.co.jp
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Fujimura
authors.forename: Mitsuyuki
authors.initials: M
authors.lastname: Hotta
mesh_terms: D000328:Adult; D000367:Age Factors; D044466:Asian People; D005123:Eye; D005145:Face / Q000502:physiology*; D005152:Facial Muscles / Q000502:physiology*; D005260:Female; D005546:Forehead; D006801:Humans; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D012212:Rheology / Q000295:instrumentation / Q000379:methods*; D015595:Skin Aging / Q000502:physiology*; D012879:Skin Physiological Phenomena; D013055:Spectrophotometry, Infrared / Q000295:instrumentation / Q000379:methods; D055815:Young Adult