Clinical evaluation of a non-ablative 1940 nm fractional laser

Non-ablative fractional lasers cause little down-time, however, some patients want more noticeable results with fewer treatments. The 1940 nm wavelength matches one of the water absorption peaks in the mid infrared band of electromagnetic energy. The skin absorption is much stronger than other non-ablative wavelengths (1410-1550 nm) and weaker than ablative wavelengths (Er:YAG or CO2). The objective of this study was to characterize clinical efficacy using this technology to treat photodamaged skin in human subjects.

Under an IRB approved study, eleven subjects with facial photodamage (1 male and 10 female) were enrolled and completed the study. The fractional 1940 nm laser was comprised of a thulium rod pumped by a pulsed alexandrite laser. The fractional patterns were generated by four separate handpieces (two dot (0.48mm and 0.76mm dot-to-dot distance or pitch) and two grid geometries) whereby a larger beam was broken up into smaller microbeams by a microlens system or reflective square grids. The low -pitch circular dot array handpiece, which is used most frequently, has a macro-spot size of 12 mm and a total applied energy of approximately 2-5 J (~ 4-10 mJ per beamlet). Contact skin cooling (5-20degC) was provided via a sapphire window at the distal end of handpiece. Pulses from the dot handpieces were applied with 20% overlap. The microspot size for the dot handpieces was ~ 0.2-0.3 mm. The two grid pattern handpieces included 0.4 mm wide lines with 45% and 0.7 mm wide lines with 65% coverage. Each subject received 3 full-face treatments 4-6 weeks apart. Anesthesia was achieved by 5% lidocaine cream and a cold air chiller. Typical treatments were carried out with two passes. Outcome assessments included changes in pigment, rhytides, laxity, elastosis, and texture, using a diffuse pigmentation scale and the Alexiades-Armenakas Comprehensive Grading Scale of Rhytides, Laxity, and Photodamage. Photographs of each patient from prior to treatment, and 3 months after treatment were analyzed by 3 blinded physician raters. A paired t-test was applied for each category comparing the pre treatment and 3-month post treatment results.

Three months after the final treatment, (a) mean pigment improvement was 21.1%, (b) rhytides were reduced by 14.3%, (c) laxity was reduced by 8.9%, elastosis was reduced by 22.3%, and (e) texture scores were unchanged. Reductions in pigmentation, rhytides, and elastosis were statistically significant (P≤ 0.05). Clinical downtime was 3-5 days. Pain was variable (mean of 2.8/10) and side effects included two cases of mild focal vesiculation. No long-term side effects were noted. Histological analysis showed focal damage that extended about 200 μm deep to the surface.

The 1940nm thulium laser is safe, well tolerated, and results in reduced downtime compared to traditional resurfacing. The study demonstrated that the 1940 nm thulium laser could achieve injury patterns capable of skin rejuvenation.