Collagen tightening induced by carbon dioxide laser versus erbium: YAG laser

Pulsed CO2 laser resurfacing improves photodamage and acne scarring by ablation of abnormal tissue with subsequent regeneration and remodeling of collagen and through heat induced collagen contraction. Whether collagen contraction persists long-term and helps maintain the skin tightening observed after resurfacing is debated. One possible mechanism of long-term clinical tightening is that of wound contracture that occurs as part of normal wound healing. If normal wound contracture, and not heat induced collagen contraction, is responsible for maintaining the initial skin tightening seen in CO2 laser resurfacing, then equal results would be expected from resurfacing with either CO2 or erbium lasers. The study was performed to determine whether there is a difference in skin tightening secondary to thermally mediated collagen contraction versus that which occurs secondary to tissue contraction of wound healing. The persistence of these changes over 6 months and the histologic characteristics were studied as well.

Nine patients had four tattoo dots applied to the upper eyelids, with horizontal axis measuring 18-20 mm and the vertical axis 6-10 mm. One month later, one eyelid was treated with three passes of the UltraPulse CO2 laser and the other eyelid with an erbium laser to the end point of early pinpoint bleeding. Three patients were treated with additional passes after pinpoint bleeding was encountered. The total number of pulses used per patient was recorded. Measurements of the vertical and horizontal distances were made after each pass and monthly for 6 months. The treated skin was then excised in performance of an upper lid blepharoplasty and the tissue submitted for histologic analysis.

In the vertical plane, the UltraPulse CO2 laser induced an average of 43% tightening intraoperatively and this gradually diminished to an average of 34% by 6 months, whereas the wound contracture of erbium resurfacing was not seen until 1 month postoperatively, at which time 42% tightening was seen, gradually diminishing to 36% at 6 months. Three patients with erbium resurfacing had scarring present. These were the three patients treated most aggressively and also the three patients with the most significant wound contracture. Scarring was not seen on the CO2 treated side in any patients. In the horizontal plane, the CO2 laser caused 31% intraoperative tightening, decreasing to 19% at 6 months. In this plane, the erbium laser induced wound contracture was 12% at 1 month which remained stable and unchanged.

Although wound contraction secondary to tissue healing may result in nearly the same tissue tightening as heat-induced collagen contraction, the two processes are very different and variable, with increased risk of scarring seen with wound contracture, compared with heat-induced collagen tightening. The tissue tightening seen with thermally induced collagen contraction is long-lasting, if not "permanent."