Treatment Types

Photofacial treatment can be categorized into two main types: ablative and nonablative. Ablative treatment vaporizes tissue at very high temperatures, whereas nonablative treatment uses gentler heat that may denature protein in certain targets but is insufficient to vaporize tissue. Photofacial treatments can be subdivided further into those that produce downtime versus those that have little or no downtime. Nonablative technologies typically do not produce significant downtime, whereas ablative treatment at a reasonable depth of treatment does. The exception is fractional ablative therapy, where tiny islands of tissue known as microscopic treatment zones (MTZs) are destroyed. The areas of normal tissue between the treated areas allow for a much more rapid healing time and little, if any, downtime (Fig. 49-1). The treatment causes macroscopic erythema and edema that typically resolves within 24 to 72 hours. The success of both ablative and nonablative laser treatments still depends on the skill of the operator. Figure 49-2 shows the pattern and depth of various treatments.

Figure 49-1 Appearance of the skin after application of the fractional laser, showing the typical areas of ablation (dots) and the spared areas in between that allow a much more rapid healing time. The treatment causes macroscopic erythema and edema that typically resolve within 24 hours. The beneficial effects of collagen contraction and skin tightening may continue for 4 to 6 months.

Figure 49-2 Diagram illustrating the difference between ablative and fractional resurfacing. A, Superficial layer of tissue is completely vaporized. B, Columns of tissue have been vaporized, leaving areas of normal tissue in between, which speeds healing. C, Nonablative fractional resurfacing, showing heated (injured) tissue that remains in the microchannels. D, Ablative fractional treatment with the tissue in the microchannels vaporized. Ablative and nonablative fractional laser treatments can essentially penetrate to the same depth; however, ablative laser vaporizes tissue, whereas nonablative laser leaves a plug of necrotic debris. E, Human skin and depth of penetration of the Fraxel laser with corresponding energy settings.

(E, Courtesy of Reliant Technologies, Inc., Mountain View, Calif.)

Ablative Laser

The two most commonly used ablative lasers are the CO₂ laser and the erbium laser. The CO₂ laser was the first to be used for ablative skin resurfacing and tends to create coagulation and significant bulk heating of the skin, and therefore carries a higher risk of complications such as hypopigmentation and permanent scarring. In skilled hands it remains the most effective way to achieve the best results in skin rejuvenation. CO₂ lasers emit light in the near-infrared region at 10,600 nm. They target intracellular water, which heats cells instantly to more than 100° C, resulting in vaporization and removal of a surface layer of cells, coagulation necrosis of cells and denaturing of extracellular proteins in a subjacent residual layer, and nonfatal damage to cells in a still deeper zone. The entire epidermis and a variable thickness of dermis are removed, with a resultant smoother skin due to heat-induced shrinkage of deeper collagen. Patients must accept post-treatment edema, burning, and crusting and an average of 4.5 months of post-treatment erythema. Traditional ablative therapy carries the risk of pigmentary changes, acne flares, herpes simplex virus infection, scars, milia formation, and dermatitis.

Erbium (Er:YAG) lasers are solid-state lasers whose lasing medium is erbium-doped yttrium aluminum garnet (Er:Y₃Al₅O₁₂). The erbium laser has become a more popular resurfacing modality than the CO₂ laser because of its precision and lower degree of bulk heating. It also targets intracellular water at 2940 nm, but it is considerably less ablative than the CO₂ laser. The ablation is more superficial and wounds heal more quickly, but it is less effective at equal fluence and with a similar number of passes compared with the CO₂ laser. To achieve an effective thermal damage effect to improve solar elastosis and rhytids, a longer pulse duration is required when using the erbium laser. A combination of erbium and CO₂ lasers may be used as an alternative to the CO₂ laser alone.

Nonablative Laser

Nonablative lasers can be used to selectively injure the dermis or a target in the skin while protecting the epidermis by cooling during treatment, such as the Nd:YAG laser used for collagen remodeling of the dermis or the treatment of leg, truncal, and facial veins. Like ablative lasers, nonablative lasers emit coherent light at wavelengths absorbed by water. This approach has less predictable efficacy compared with ablative laser techniques.

Fractional photothermolysis using the erbium laser has been developed to overcome the disadvantages of conventional ablative and nonablative laser therapies. It produces columns of thermal damage or ablation called foci, or MTZs, ranging between 50 and 150 µm in diameter and located at specific depths from 0 to 550 µm (Fig. 49-3). Treatment time for each pulse (exposure duration) ranges between 3 and 30 milliseconds. The density of treatment corresponds to the inter-MTZ space and is adjustable. Because the MTZs are surrounded by uninjured tissue, keratinocytes have a shorter migration path and healing is much quicker (Fig. 49-4). The technique coagulates both the epidermis and dermis without affecting the stratum corneum, which acts as a natural bandage that protects the tiny wounds as they heal. To improve solar elastosis, scars, and rhytids, a course of treatments, typically three to five, is spaced at least 2 weeks apart. The treatments have fewer and less severe side effects than traditional, nonfractional ablative resurfacing and, with the exception of deep rhytids, the results in terms of skin tone, texture, dyschromia, and scars are essentially equivalent. More aggressive CO₂ laser fractional treatment vaporizes tiny columns of tissue entirely and may require fewer treatments than erbium devices, but it causes more downtime because of erythema and even crusting that can last a few days, with a possible higher incidence of postinflammatory hyperpigmentation. The ratio of risk to benefit always must be considered when choosing the appropriate device for the condition to be treated.