As discussed earlier, before Van Gemart proved the depth capabilities of the 532 nm KTP laser, the general attitude was that the high absorption coefficients of the competing chromophores such as melanin would not allow the laser to penetrate to a sufficient depth to treat vascular conditions. Although this was disproved, the fact remains that there is a large amount of melanin absorption at the 532 nm wavelength. This creates an ideal condition for the treatment of lentigines, freckles, and macular seborrheic keratosis on skin types I-IV. (Figure 4.4 , showing treatment with Palomar Lux G hand piece, demonstrates the type of lesion being discussed.)
Treatments are performed using a 2-4 mm spot size, a pulse duration of 10-15 ms, and a fluence of 15-20 J/cm2. The immediate endpoint is a darkening of the lesion, which may occur over the following 10 minutes. In many cases, especially with lighter pigment, a second pass may be necessary. The lesion will develop a micro-crusting type of reaction, and will come to the surface of the skin and basically exfoliate off the epidermis. This will occur over a period of 5-10 days after treatment.
Complications can arise when using KTP lasers in basically the same manner as any other laser system. Undercooling, overtreatment, and misplacement of hand piece aperture can all cause minor side effects. When improper contact is made with the skin, the cool tips cannot do their job, and a burn may follow. Too much overlap can cause blistering and burning as a result of too much thermal damage in one place. Side effects are more common when treating
patients in the IV-VI skin-type range, as a result of the high melanin absorption level at 532 nm, so generally only skin-type I-IV are safely treated. Most issues can be resolved with topical steroids, ice, and proper postcare.
Intense pulse light (pulsed light) is another very effective method of treating unwanted epidermal pigment. This technology is discussed in detail later in this chapter.