In Vivo Histological Study Evaluating Non-Ablative Fractional 1940-nm Laser.

Objectives: Non-ablative fractional lasers (NAFL) have increased in demand compared to ablative laser treatments as they provide lesser down time, fewer side-effects, and are safer to use. Non-ablative fractional treatment with lasers ranging from 1320 to 1927-nm have been shown to be safe and effective for skin resurfacing procedures. The objective of this study is to investigate healing of the 1940-nm NAFL-induced microthermal treatment zones (MTZs) in human skin from a histologic perspective.

Methods: Three subjects received 1940-nm NAFL treatment to test areas on the abdomen at various timepoints during the study. The minimum 5 mJ/MTZ and maximum 20 mJ/MTZ energy settings were used at 20% coverage. Biopsies were taken coinciding with immediately posttreatment, 1, 3, 7 days, and 6 weeks posttreatment. Blinded analysis of hematoxylin and eosin stained slides was performed to measure the width and depth of the MTZs and evaluate the inflammatory and healing response of the skin over time (immediately to 6 weeks posttreatment). Safety was evaluated by assessing local skin responses and adverse events immediately after treatment and at all study visits.

Results: Histological analysis of tissue following NAFL 1940-nm treatments showed mild early inflammatory response (presence of lymphotic infiltrate) in some test areas and zones of necrosis and coagulation having widths and depths (immediately-3 days posttreatment) that scaled with the 1940-nm pulse energy. Signs of healing such as presence of dermal mucin, evidence of fibrosis, and absence of necrosis were observed long-term (7 days to 6 weeks posttreatment). Evidence of the MTZ persisted beyond the 6-week study and was predicted to last for 100 days. All local clinical skin responses healed within 6 weeks and were limited to mild, transient erythema and edema which resolved in less than 12-24 h following treatment. No serious adverse events occurred during the study.

Conclusions: NAFL 1940-nm treatments are safe for inducing small fractional coagulation and necrosis zones in abdominal skin. NAFL 1940-nm laser creates fractional columns of injury with sufficient depth and coverage that suggest effective skin resurfacing, like other non-ablative fractional lasers.