title: Repetitive Er:YAG laser irradiation of human skin: a histological evaluation.
abstract: OBJECTIVE
  Deep coagulation of skin collagen by Er:YAG laser repetitive pulses has been predicted by previous theoretical models and later demonstrated on animal skin. The goal of this study was to determine the effect of repetitive Er:YAG laser pulses on human skin and its response to this treatment.
  
  
  METHODS
  Lid skin of six female volunteers with blepharochalasis has been treated with laser at day 0, 7, and 21 before elective surgery-blepharoplasty. The treated skin was excised as part of the procedure and prepared for further histological examination. We used a 2,940 nm Er:YAG laser (Fidelis M320A by Fotona) with 'smooth' mode parameters: fluence from 0.50 to 2.00 J/cm2; six pulses per packet; 550 microsecond/pulse, 250 millisecond/packet; single pass, no overlapping; spot size 5 mm; repetition rate 20 Hz.
  
  
  RESULTS
  We observed deep collagen denaturation at laser fluences of 1.25 J/cm2 and over; epidermal damage was proportional to fluence with total coagulation of the epidermal layer at fluences of 1.75 J/cm2 and over. At day 7 after laser treatment we observed a complete regeneration of the epidermal layer and a regeneration zone within the dermis with prominent infiltration of CD68+ monocytes/macrophages. At day 21 after laser treatment we observed collagen remodeling and (myo-)fibroblast proliferation at tissue depths of up to 240 microm.
  
  
  CONCLUSIONS
  Repetitive Er:YAG laser irradiation is effective in deep denaturation and remodeling of human skin collagen in vivo, with less epidermal damage compared to standard Er:YAG laser skin resurfacing.
authors.affiliation: Department of Oculoplastic Surgery, University Eye Clinic, Medical Centre, Ljubljana, Slovenia. brigita.drnovsek@kclj.si
authors.forename: Brigita
authors.initials: B
authors.lastname: Drnovsek-Olup
authors.forename: Matej
authors.initials: M
authors.lastname: Beltram
authors.forename: Joze
authors.initials: J
authors.lastname: Pizem
mesh_terms: D005260:Female; D006801:Humans; D007834:Lasers; D008875:Middle Aged; D012867:Skin / Q000473:pathology* / Q000528:radiation effects*; D013997:Time Factors