One of the earliest applications of lasers in medicine was Leon Goldman’s use of the ruby laser to treat pigmented lesions in 1963. At that time, the ability of a normal-mode ruby laser with a 0.5 ms pulse duration was noted to selectively destroy pigmented structures in the skin.1 Although seemingly ironic in hindsight, the field of laser dermatology then shifted to the use of continuous wave modalities such as the carbon dioxide laser (10,600 nm) and the argon laser (418 nm), which were used in a non-selective fashion to treat pigmented lesions. Needless to say, the results were often unpredictable, with complications such as scarring and dyspigmentation.
A new era in the laser treatment of pigmented lesions arrived when R. Rox Anderson and John Parrish of Massachusetts General Hospital described the theory of selective photothermolysis,2 which provided laser surgeons with a platform on which to perform the selective treatment of pigmented lesions. More recently, fractional photothermolysis has been introduced to non-selectively improve the appearance of certain types of undesirable pigment,3–7 but this time without the risks and downsides of the continuous wave lasers.
LASERS AND IPL SOURCES USED TO TREAT BENIGN PIGMENTED LESIONS
Melanosomes have a size range of roughly 0.5 to 1.0 μm, which translates into a thermal relaxation time in the nanosecond to microsecond range. Clinically these structures can be targeted through the use of Q-switched lasers (QSLs). QSLs store large amounts of energy in the optical cavity through the use of an optical shutter. When the laser is fired, it releases high-powered pulses of extremely short duration, in the nanosecond range,8 resulting in a photomechanical tissue reaction. QSLs are the current modality of choice in the treatment of pigmented lesions. While most lesions can be significantly improved, complete clearance may be difficult to achieve and there is no guarantee that the skin will appear normal after treatment. In addition, the operator’s ability, clinical knowledge, and training in the laser device are major factors affecting the outcome of treatment.
Currently, six wavelengths of QSL are available, which include the Q-switched ruby laser (694 nm), the Q-switched alexandrite laser (755 nm), the Q-switched Nd:YAG laser (1064 nm), the Q-switched frequency-doubled (FD) Nd:YAG laser (532 nm), and the Q-switched Nd:YAG laser with dye handpieces (585 and 650 nm). Many QSLs are also capable of operating in a microsecond mode, which can be used to target melanosomes.
Although long-pulsed (LP) lasers (pulsed dye laser [PDL] at 585–595 nm, LP ruby at 694 nm, LP alexandrite at 755 nm, LP Nd:YAG at 1064 nm, and LP diode at 800 nm) have pulse durations that are in the millisecond domain, they are capable of targeting melanosomes in clinical practice because melanosomes have a tendency to cluster together, particularly ...