A preliminary study of dye-enhanced laser photosclerosis

Laser ablation of veins after injection of wavelength-specific dyes to enhance and localize energy absorption could provide a useful adjunct to current treatment options. To enhance the absorption of diode laser energy at 808 nm, ear veins of 41 rabbits were infused with 2 to 3 ml of indocyanine green dye (maximum absorption, 805 nm) and exposed for 2 to 20 seconds. Animals were killed between 0 and 28 days after operation. Discrete time intervals of laser exposure exist during which various-sized vessels can be ablated without significant thermal injury to the overlying tissue. Small vessels (0.2 mm in diameter) blanch after 2 to 3 seconds of exposure, whereas medium-sized vessels (2 mm in diameter) require 8 to 10 seconds. Vessels can be ablated with a power density as low as 11.1 W/cm2. Specimens taken immediately after laser exposure show vessel wall thinning and a reirradiation effect, created as laser energy initially absorbed by dye is reemitted. By the seventh day after operation, a brisk inflammatory response and acanthosis of the overlying epidermal layer develop. The lumen is partially filled by thrombus with cellular invasion. By postoperative day 28, the epidermal thickening and inflammatory reaction have resolved; the vessel walls are fibrotic. The use of low-power, air-cooled diode lasers, in conjunction with wavelength-specific dyes, may provide a simple, viable, and cosmetically appealing alternative to the treatment of superficial varicosities of the extremities.