Epidermal Fluence Threshold Determination by Real-Time Melanin Measurements

Epidermal preservation is essential during laser treatment for vascular, hair, and benign pigment dyschromias. Epidermal tolerance is determined by epidermal melanin content, fluence, pulse width, wavelength, skin cooling, and spot size. The authors' objective was to determine the maximum epidermal tolerance for the long-pulse alexandrite 755 nm and the long-pulse neodymium-doped yttrium aluminum garnet (Nd:YAG) 1064-nm lasers for varying epidermal melanin content.

Skin melanin measurements were performed at the test sites with a melanin reader, and 0.5 to 1 second of refrigerated air precooled the skin. Then, alexandrite and Nd:YAG laser test spots of 5 to 18 mm were delivered in a series of ascending fluences using 5-, 20-, and 50-ms pulse widths. Skin response at 24 to 48 and 96 hours was scored from 0 to 15 varying from "no reaction" to "severe scabbing."

Alexandrite laser, mean threshold fluences increased by a factor of 1.2 increasing from 5 to 20 ms, and by a factor of 1.4 increasing from 5 to 50 ms, among subjects with a melanin index (MI) from 9 to 25 (Fitzpatrick skin phototype I-III). The Nd:YAG fluence to reach epidermal tolerance was 6X the fluence with the alexandrite laser for the same MI in subjects with MI 26 to 35.

Epidermal melanin measurements are quantitative and objective, therefore, improving treatment setting determination by decreasing the risk of overtreatment or undertreatment.