The basic science of current laser systems was described in 1916 when Einstein proposed his theory of spontaneous and stimulated emission of radiation. In the 1950s, building on Einstein's theory, Schawlow and Townes created a device called a MASER (microwave amplification by stimulated emission of radiation). This device intensified a beam of microwaves. In 1957, they decided to produce a similar device that would amplify much shorter, visible light, an optical laser. Simultaneously, Theodore Maiman was working on such a device at the Hughes Corporation in California. Using a synthetic pink ruby crystal, he succeeded in producing the first optical MASER in 1960. It amplifies light rather than microwaves and was given the name LASER. To demonstrate the power of this light beam, the millisecond pulse of light was used to drill a tiny hole through a stack of razor blades. It was reportedly suggested that the power of the laser should be measured not in “watts” but in“Gillettes.” In the next 4 years, there was a rapid proliferation of laser invention. In 1961, Java et al. developed the helium neon (HeNe) laser, and Johnson developed the neomydium:yttrium-aluminum-garnet (Nd:YAG) laser. The argon laser (blue-green visible beam) was developed in 1962 by Bennett. In 1964, Pate et al. developed the carbon dioxide laser. These lasers, developed in only 4 years, represent the mainstay of lasers in use at this writing.
A laser comprises several key components, including an energy source, a laser medium (gas or solid state), and a laser cavity (resonator). Lasers involve light energy, which is defined by the electromagnetic spectrum(Fig. 1). The electromagnetic spectrum involves anything from AM radio, shortwave, VHF, VHF radar, infrared, visible light, ultraviolet, x-rays, and gamma rays. The frequency of a laser goes a long way to determine its characteristics. In a laser system, an element or compound is energized. The purpose of this is to excite electrons into a higher-energy state, which means an unstable orbit around their nucleus. As these electrons disintegrate into their more stable state, they give off a unit of energy called a photon. A photon has a characteristic wavelength. These photons are emitted in brownian motion inside the resonator. As they are bouncing around, they hit other molecules, prompting other electrons to move to their stable state, giving off more photons of energy. Their first situation is a spontaneous emission resulting from molecular changes; the second one is a stimulated emission(Fig. 2). Inside the resonator, the photons are reflected off mirrors at either side of the resonator. One of the mirrors is totally reflective; the other is not completely reflective. Photons of energy are allowed to egress through this side because these photons all have the same wavelength and are parallel. They now become a laser beam. A homogeneous light source is intense because it is a pure form of light energy(Fig. 3). It is coherent because it has only one wavelength. It is collimated because the beams are parallel. (It does not spread as a normal light source.) This produces the basis and characteristics of laser energy.
When laser light contacts the target, the interaction will depend on the wavelength and the composition of the target substance. The energy may bereflected. For instance, when light cannot be absorbed or pass through (e.g., contact with metal), it bounces off. The light may betransmitted, e.g., passing through glass unchanged. The light may berefracted (direction of light change) or scattered (light dispersed randomly). Laser light may be absorbed. When laser light passes through tissue and is absorbed by the target, the clinical result is maximized. Research and development of lasers have concentrated on creating lasers that can be absorbed selectively by the desired target substance. These target substances are known as chromophores. Primary chromophores in the skin are hemoglobin, melanin, and water, and they form the basics of most of the lasers used in plastic surgery. Chromophores may be from an exogenous source such as tattoo pigments. When a particular wavelength has a predominant chromophore in the skin, it is highly absorbed by it. There is minimal scatter of the laser light, and the desired clinical result is maximized. The use of lasers in cutaneous problems advanced with the concept of selective photothermolysis. Initially, there were lasers and there were problems, and lasers were aimed at problems such as vascular anomalies. For example, the argon laser was known to be absorbed by hemoglobin and was used to treat vascular anomalies. It is also quite well known that at that particular wavelength there was quite a bit of absorption from melanin pigments. Because of this, almost every patient treated with an argon laser for a vascular malformation had hypopigmentation. An effort was made to develop a laser that would be absorbed by hemoglobin and not as much by melanin. In other words, the laser energy was aimed at a very specific target in an effort to prevent collateral damage, and this was the theory presented by Anderson and Parrish.1 We now have developed more refined lasers that will selectively eliminate pigmented lesions or vascular lesions. Other lasers, such as carbon dioxide lasers, are absorbed by water and hence are used to vaporize lesions, destroy very finite layers of skin, or act as a scalpel.
It should be kept in mind that despite all these applications, lasers only have the ability to increase the temperature of the targeted chromophore. A small increase in temperature is used in photodynamic therapy to selectively destroy cancer cells, for example. Vascular and pigmented lesion lasers are instruments that photocoagulate, while a continuous-wave carbon dioxide laser produces photovaporization when it contacts water (Table I).
The second part of selective photothermolysis relates to the exposure time of the light (pulse width). Thermal diffusion is limited if the pulse width is less than the thermal relaxation time of the tissues. By developing lasers that have wavelengths highly specific to the target tissue and are pulsed to match thermal relaxation times of specified tissues, laser therapy has become more refined (Fig. 4). Undesirable tissue damage, which leads to delayed healing and scarring, has been minimized. Available treatments for cutaneous pathology have expanded, with results being consistently favorable. Many lasers are available for clinical use. The lasers commonly used in plastic surgery are summarized in Table II.
In the hands of experienced and cautious users, the laser is a very safe tool. General safety guidelines as well as manufacturer recommendations for specific lasers must be observed. Eye protection is essential. Goggles are available for protection from each of the therapeutic wavelengths and, for the most part, are not interchangeable. Patients' eyes are protected with corneal shields when treatment involves the face. Limited access to the laser is achieved by posting “Laser in Use” signs at the entry to the operating arena. Keys are required for accessing the laser itself and should be available only to qualified personnel. Standby modes built into the machines are helpful for preventing accidental firing. Common-sense rules regarding electricity and water apply to the use of lasers. The operating room environment should be one that restricts combustible agents. Fires involving surgical drapes and hair have been reported in oxygen-rich environments when the laser is used around the face. Plume (smoke) evacuation is essential during most procedures. This is accomplished with the use of smoke evacuators. Standard wall suction is not sufficient.
Vascular lesions are among the most commonly treated by laser. Selective photothermolysis1 has revolutionized the treatment of most vascular lesions and allowed for treatment of not only adults but also infants and children with minimal risk of scarring.
Numerous authors have reported excellent results in the treatment of port-wine stains in children. Tan et al.2 reported complete clearing of pink-red marks in 35 children under the age of 14 with an average of 6.5 treatments with the Candela flashlamp-pumped pulsed-dye (FLPPD) laser. Reyes and Geronemus3 reported a series of 73 patients (aged 6 months to 14 years) treated successfully, with overall improvement after one treatment of 53 percent. Greater than 75 percent fading was seen with an average of 2.5 treatments in 33 patients. Morelli and Weston4 advocate early treatment (7 to 14 days), with completion of treatment by age 6 months. In their series of 132 patients, 25 percent of patients cleared prior to 18 months, while only 7 to 10 percent were cleared if treatment started after 18 months with similar numbers of treatments (7.8 and 7.0, respectively). Goldman et al.5 confirmed that early treatment leads to improved results. Ashinoff and Geronemus6 published similar results and showed that treatment can be done safely in infancy.
Pigment changes may be seen but resolve in 3 to 6 months. While previous work with the argon laser sometimes resulted in scarring, this is very rare with the flashlamp-pumped pulsed-dye laser. Lesions of the face and neck respond better than those of the trunk or extremities.
Port-wine stain treatment in adults is equally successful. Prior to the late 1980s, treatment in childhood was not available, so many persons have reached adulthood without treatment. Numerous authors have reported successful treatment with the flashlamp-pumped pulsed-dye laser.7-9 As with children, there are varying results depending on the anatomic location.
There is pain associated with flashlamp-pumped pulsed-dye laser treatment. Most adults find the level of pain during treatment tolerable. Some require intravenous sedation or intramuscular preoperative medication. EMLA cream is a helpful adjunct and may be used prior to the procedure. General anesthesia is recommended for infants and small children.
Arterial malformations are complicated and require extensive workup. Treatment usually includes superselective embolization combined with surgical excision. Laser therapy may be a useful adjunct in these cases. It may decrease bleeding during excisional surgery. The superficial components of the malformation may be treated with the flashlamp-pumped pulsed-dye laser. Intralesional laser therapy holds promise for treatment of vascular malformations and massive hemangiomas.10 At this time, clinical experience is limited.
Treatment of hemangiomas (strawberry mark) with lasers has met with controversy. Numerous authors report the use of argon and YAG lasers,11-13 citing their ability to arrest the growth and/or induce the involution of hemangiomas. For some reason this has not been widely accepted, despite extensive documentation. More recently, the pulsed-dye laser has been reported as a useful tool for the treatment of hemangioma.14-16 Its value is clearly limited to the cutaneous component or telangiectasia associated with the hemangioma or very flat lesions. Intralesional treatment with the KTP(potassium-titanyl-phosphate) bare fiber has been very effective in recent cases.
Tattoos and Pigmented Lesions
The treatment of pigmented lesions and tattoos also has been revolutionized by the theory of selective photothermolysis.1 Prior to this, laser therapy of these conditions was fraught with difficulty, most noticeably including unacceptable scarring. Decorative tattoo removal is quite successful utilizing various Q-switched lasers17-20(Table III). Pigments respond with variable success. A multicolored tattoo may require treatment with various wavelengths to maximize pigment removal.
Traumatic tattoos are also removed very successfully with the Q-switched ruby or Q-switched alexandrite lasers.21-23 This is accomplished without scarring.
Cosmetic tattooing has become popular in the last decade. When removal is desired for misplacement or other reasons, laser therapy has been sought. Q-switched lasers can be used to remove cosmetic tattooing; but although this has been successful, there are limitations and possible complications. White tattoo pigment responds poorly to laser treatment. Anderson et al.24 report darkening of cosmetic tattoo ink immediately following laser treatment. While the chemical reaction is not understood, the darkening is attributed to the reduction of ferric oxide(Fe2O3, “rust”) to ferrous oxide (FeO, “jet black”). This potential complication may be irreversible.
Pigmented lesions such as nevus of Ota are treated successfully with the Q-switched ruby laser and the Q-switched YAG laser.25,26
Scars and Dermatologic Conditions
Hypertrophic scars may be flattened and lightened by the use of the flashlamp-pumped pulsed-dye laser. Alster27 demonstrated improvement in the clinical, histologic, and textural appearance of both hypertrophic and erythematous scars. While not fully understood, the improvement is presumed to be from the direct effect of the laser on the dermal blood vessels.
There may be an effect on the adjacent collagen turnover. Dierickx et al.28 reported on 15 patients with erythematous/hypertrophic scars and 11 with postinflammatory hyperpigmentation. All patients benefited from treatment, and no adverse sequelae were seen. Hypertrophic scars were improved an average of 77 percent, with the number of treatments ranging from one to four. The hyperpigmentation group improved an average of 80 percent with one to two treatments.
A wide variety of other dermatologic conditions may be treated with lasers(Table IV). Nevi have been treated by some physicians with various lasers. While lesions can be removed, histologic study and control are compromised. Any lesion with premalignant or malignant potential should be biopsied and fully excised by traditional methods.
Uvulopalatoplasty with laser has been reported for the relief of snoring with promising results.29 Micro-hair transplantation with the ultrapulsed carbon dioxide laser has been reported. Advantages cited are decreased time of grafting and decreased swelling and bleeding.30 The question remains whether graft viability is helped or hindered by this method.31-32
Warts may be treated with flashlamp-pumped pulsed-dye lasers. Kauvar et al.33 have reported 83 to 99 percent resolution(depending on anatomic location) with 3- to 9-month follow-up. The carbon dioxide laser also has been used. Adequate smoke evacuation is necessary to minimize the risk of viral transmission by the laser plume.
Laser use as a scalpel for cosmetic surgery has been controversial. Mittleman et al.34 evaluated human tissue injury caused by various lasers in facial surgery and compared this with conventional electrocautery and blade. They documented histologically that lasers(CO2, KTP, and Nd:YAG) resulted in more tissue injury than cold steel techniques. Clinically, the lasers were superior to the scalpel for hemostasis. This study looked at acute effects only. They did not examine healing of the wounds or long-term effects. The depth of laser damage is as follows:
- CO2: 0.50 mm epithelial, 0.20 into dermis
- KTP: 0.52 mm epithelial, 0.40 into dermis
- Nd:YAG: 0.70 mm epithelial, 0.45 into dermis
- Cautery: 0.75 mm epithelial, 0.20 into dermis
Laser blepharoplasty has been reported35,36 with mixed results. A survey by Glassberg et al.37 of more than 4000 cases cited advantages of decreased edema, ecchymosis, and postoperative pain, with no serious event documented by the survey responders.
Resurfacing of photoaged and finely wrinkled skin is the most recent application of the laser in plastic surgery. Treatment of rhytids is accomplished with recently developed carbon dioxide lasers. This new generation of lasers is based on the theory of selective photothermolysis.1 The rapidly pulsed laser allows controlled destruction of unwanted cells. This technique is being used as an alternative to chemical peeling and dermabrasion.
Patients with fine wrinkles, “lipstick lines,” and photoaged skin may benefit. All skin types can be treated, but treatment regimens vary. Light-skinned persons with fragile skin are treated very superficially. Those with darker skin types are pretreated with a bleaching agent to prevent hyperpigmentation postoperatively. History should include findings related to keloid formation, herpes, Accutane use, and previous procedures to the face. Herpes prophylaxis is recommended for all patients and is most important with a positive history. Accutane use 12 to 18 months prior to treatment puts the patient at risk. Reepithelialization is compromised, and scarring is believed to be more prevalent. Previous procedures to the face may have resulted in imperfections that can be magnified after resurfacing. These areas should be pointed out to the patient prior to treatment.
Various carbon dioxide lasers are now available for resurfacing. The distinction of this new technology is the rapidly pulsing rather than continuous-wave laser light in the first-generation carbon dioxide lasers. Resurfacing lasers may be hand held or equipped with a computerized scanning device.
Preoperative skin regimens for 3 weeks prior to treatment are suggested. Realistic expectations will avert many difficulties postoperatively. The patient must be well informed and aware that healing may take up to 2 weeks. In addition, redness may persist for 6 to 8 weeks. Intraoperatively, safety guidelines for the particular laser being used are strictly adhered to. Postoperatively, a closed dressing or open (Vaseline and vinegar soaks) technique of wound care may be followed based on the surgeon's preference. Sun exposure is to be avoided. The preoperative skin care regimen is resumed when healing is complete. Any early signs of scarring are treated promptly with topical or intralesional steroids. Hyperpigmentation is treated with hydroquinone or other bleaching agents.
In addition to eliminating fine rhytids, there is a secondary phenomenon that occurs following laser resurfacing that has been termed collagen shrinkage. This phenomenon has been noted in the cornea for many years.38-40 While this phenomenon has been reported anecdotally, study of it in the skin has been limited. There are two early reports on collagen shrinkage in a skin model. Ross et al.41 reported on the in vivo dermal collagen shrinkage and remodeling following carbon dioxide laser resurfacing. A 10 to 30 percent reduction in the area treated was observed immediately after laser exposure. The magnitude of shrinkage increased with fluence and with the number of ablation passes. Thermal damage was assessed histologically, but correlation with shrinkage data is pending. Gardner et al.42 demonstrated in vitro temperature changes with both the Ultrapulse and the SilkTouch. Histologic studies showed that laser treatment resulted in changing the order and distinctness of the collagen bundles. The authors concluded that laser treatment leads to significant changes in the appearance and mechanical properties of dermal collagen that contribute to the clinical changes observed with cutaneous resurfacing.
Is resurfacing better than peels or dermabrasion? Fitzpatrick43 compared pulsed carbon dioxide laser treatment with trichloroacetic acid (35%), Baker-Gordon phenol (50%), and dermabrasion. This comparative clinical and histologic study involved a porcine model. The phenol-treated site took 3 weeks to heal in contrast to the laser-treated sites, which healed in 7 days. Trichloroacetic acid was comparable with laser with 150 mJ (three passes) or 250 mJ (one to two passes). Dermabrasion was comparable with laser at 250 to 450 mJ (two to three passes).
Improvement in loose skin of the cheeks and nasolabial folds and in redundant eyelid skin has been seen following laser resurfacing. This response is not noted after peeling or dermabrasion. Many physicians recommend a full-face treatment to take advantage of overall tightening of the skin. As discussed previously, the reasons for this are not fully understood and are currently being studied.
Complications of resurfacing include pigment changes, itching, milia, hypertrophic scarring, and ectropion (so far, transient). A misaimed laser, of course, can cause significant damage to the skin or corneal damage.
A wide variety of lasers provides the plastic surgeon with treatment options that were not available previously. Appropriate, safe use of lasers complements the many therapeutic treatment options available to plastic surgeons. Lasers have introduced a new therapeutic modality. Because of the ways the skin and its defects may be altered with lasers, they will be an increasingly important part of plastic surgery.
Bruce M. Achauer, M.D.
University of California; Irvine Medical Center; Division of Plastic Surgery; Rte. 81, Bldg. 53; 101 City Drive South; Orange, Calif. 92868
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