Lasers and Optical Technologies in Facial Plastic Surgery

Lasers, optical devices, and related technologies play an increasingly significant role in aesthetic and reconstructive surgery. The most appealing feature of optical technologies is that their effects are localized to the region of light distribution, resulting in the ability to target specific structures and/or tissue layers within the skin or mucosal surfaces.¹ Furthermore, the tissue effects of these devices can be customized by adjusting the fluence rate, application time, and spatial parameters. Lasers and optical technologies allow precise control over the temporal and spatial evolution of heat and/or distribution of radiant energy to activate thermal, mechanical, or chemical processes. This review seeks to offer a panoramic view of the history of optical technologies, highlighting essential developments as applied to facial plastic surgery in the last 10 years, later transitioning into a discussion of future trends and emerging optical technologies related to facial plastic surgery.

Ablative Laser Therapy. Aging skin is characterized by excess rhytides and laxity. Over the past 10 years, a mainstay of skin rejuvenation has been laser resurfacing. Laser skin resurfacing was first described in 1985, following carbon dioxide (CO₂) laser treatment of actinic cheilitis that unintentionally resulted in dramatic cosmetic improvement of the treated lip.^{2 - 3} Laser skin resurfacing is ablative and relies on the selective photothermal destruction of specific layers of the epidermis and dermis combined with a limited or controlled depth of residual thermal injury. The interaction achieves thermal confinement, resulting in laser pulse durations that are shorter than absorbed photothermal energy dissipation time, an effect that promotes highly localized heating.⁴ Heat induces dermal remodeling with new collagen synthesis and collagen contraction.^{5 - 7} Ablative laser therapy has largely replaced the widespread use of chemical peels, which depend heavily on individual skin diffusion properties that are widely divergent among different facial regions and different people. In contrast, laser resurfacing produces fairly homogeneous and repeatable results.^{8 - 12} Laser skin resurfacing works best for patients with fair skin, while the results for patients with darker skin are less predictable and prone to pigmentary changes.¹³

Presently, both CO₂ and erbium:YAG lasers are used for skin resurfacing. For most pulse durations, the CO₂ laser creates a zone of thermal injury up to 200 μm in depth, leading to prolonged erythema and slower recovery times. In contrast, the use of an erbium:YAG laser (pulse length, approximately 250 microseconds)^{14 - 16} has advantages such as relatively quick recovery times, much less erythema,^{17 - 21} higher light absorbance, and the production of less thermal injury with each pass (approximately 50 μm). However, slightly decreased clinical efficacy is also associated with the erbium:YAG laser.^{22 - 23} Resurfacing has also been performed using combinations of laser devices (eg, erbium:YAG and CO₂ lasers),^{24 - 29} laser and botulinum toxin injections,^{30 - 32} laser and traditional facial plastic surgery procedures,^{33 - 40} and laser and metallic-based skin care products.⁴¹ Laser resurfacing has also been used to treat rhinophyma,^{42 - 44} tuberous sclerosis,^{45 - 48} and many other disorders^{49 - 53} and to assist in scar revision.^{54 - 58} Research in resurfacing has largely focused on understanding the mechanisms of action with the aim of optimizing the efficacy of procedures.^{10 ,59 - 77}

Nonablative Laser Therapy. While ablative laser skin resurfacing is in many ways safer and more predictable than the chemical peels that it has supplanted, its consequent epidermal and dermal destruction leads to prolonged recovery times and the potential for complications.⁷ Nonablative resurfacing aims to selectively heat dermal tissues, while sparing the epidermis from significant thermal injury, and thus to reduce complications and recovery times.^{7 ,23 ,78 - 88} Nonablative therapies rely on the selective heating of regions of tissue within the dermis, which is accomplished by using lower laser fluence rates or by protecting the epidermis using cryogen spray,^{89 - 90} contact,^{91 - 93} or air⁹⁴ cooling. Diode lasers (532,⁸⁰ 900,^{95 - 97} and 1450^{98 - 102} nm), rare earth lasers such as Nd:YAG lasers,^{79 ,88 ,103 - 110} and pulsed dye lasers (PDLs)^{85 ,88 ,102 ,110 - 114} have all been reported to improve skin appearance and textures. Accordingly, nonablative therapies have been used in combination with other cosmetic procedures.^{95 - 97 ,115 - 116}

Other Nonablative Technologies. Radiofrequency (RF) devices are perhaps the most commonly used nonoptical nonablative technology for the treatment of rhytides and skin laxity.^{117 - 119} Thermage (Thermage Inc, Hayward, California) is the archetype cosmetic RF procedure, achieving spatially selective heating through 2 simultaneous processes: the heating of tissue with RF energy and surface cooling with cryogen spray. The subdermal remodeling of collagen induced by the Thermage treatment contributes to improvements in skin laxity and texture,^{120 - 126} although complications have also been reported.^{127 - 128}

Radiofrequency has also been used in corrugator supercilii motor nerve ablation for the elimination of glabellar furrowing,¹²⁹ a condition that is commonly treated by surgery^{130 - 131} or by botulinum toxin.¹³² Other nonablative resurfacing technologies that have been studied include high-frequency focused ultrasound,¹³³ which has been used to specifically target and tighten the superficial musculoaponeurotic system in the face¹³⁴ or subcutaneous fat,¹³⁵ and intense pulsed light, which will be discussed below. Recently, plasma skin regeneration devices have been introduced to achieve resurfacing by selectively heating the dermal layer with plasma energy.^{136 - 139} These devices, exemplified by the Portrait system (Rhytec Inc, Waltham, Massachusetts), represent the newest generation of nonoptical nonablative resurfacing technologies.

Intense Pulsed Light. Intense pulsed light therapies use full-spectrum, broadband light that is emitted from its flash lamp source, producing infrared wavelengths that can penetrate deeply within the skin and heat subsurface tissues. Its main advantage over lasers is its ultralow cost and short downtime, while having a moderate effect on improving the skin,^{140 - 143} possibly by the same dermal remodeling mechanism that attributes to the success of laser skin resurfacing.¹⁴⁴ In contrast, other studies have negated the efficacy of intense pulsed light, observing minimal morphological changes in dermal collagen¹⁴⁵ and no significant elimination of rhytides.¹⁴⁶

Epidermal Cooling. Epidermal cooling was the most important advance in laser skin surgery during the past 10 years. Until cooling mechanisms were introduced, most optical devices generated heat at the surface unless specific chromophores such as tattoo ink or hemoglobin (eg, port-wine stain) were targeted. Surface cooling, in combination with laser heating, solved this problem by facilitating the creation of subsurface temperature elevations, while maintaining the surface at appropriate temperature levels (eg, near ambient). For rejuvenation, selective heating of the dermis and subdermal collagen was achieved.⁹⁰

The most effective cooling mechanism is cryogen spray cooling. Cryogen cooling is used both in nonablative resurfacing and in the treatment of pigmented lesions, where epidermal protection allows the use of greater laser fluences. In treating vascular lesions, Nelson et al^{147 - 154} pioneered the successful use of cryogen cooling and PDL for treatment of port-wine stains and hemangiomas,^{155 - 156} and this technology has consequently been used in aesthetic applications.^{89 - 90} Cryogen spray cooling has also been used as an adjunct to laser hair removal to allow delivery of greater fluences to deeper depth.^{157 - 158} Other popular cooling mediums that have been used with varying efficacy in conjunction with nonablative laser therapy include the sapphire contact cooling device,^{91 - 93} based on direct conductive cooling, and cold-air cooling,^{94 ,159 - 160} which relies on convective cooling and could mitigate complications associated with ablative laser therapy.

Fractional Ablation. Fractional ablation, which is the most recent development in laser skin resurfacing, has existed conceptually for quite some time, though not implemented in practice. The term fractional photothermolysis was first coined by Manstein et al¹⁶¹ in 2004. In fractional ablation, laser spots are small (approximately 100 μm) and are separated from one another by a considerable distance. Small regions of tissue injury (and hence remodeling) exist as islands surrounded by normal skin. Reepithelialization is rapid.¹⁶¹ The most popular fractional ablation devices operate at 1550 nm (Fraxel, Reliant Technologies, San Diego, California).^{161 - 165} Aside from being primarily used as a resurfacing tool,^{161 - 162 ,166 - 168} fractional photothermolysis has been used to treat pigmentation lesions,^{169 - 173} acne scars,¹⁷⁴ and surgical scars.¹⁷⁵ Complications and adverse effects are short-term and usually limited to erythema, skin dryness, and facial edema.^{176 - 177} Fractional photothermolysis is generally associated with a relatively high patient satisfaction rate, as high as 75% according to Cohen et al.¹⁷⁸

The main challenge for skin resurfacing in the future will be to achieve a long-term natural-looking substantial improvement in skin quality. Also, resurfacing and related technologies will strive toward achieving more dramatic results and supplant or postpone the need for traditional aging face procedures such as rhytidectomies and blepharoplasties.^{118 - 120 ,122 ,134 ,179} Finally, home-use, optically based skin therapy devices will be developed to safely allow patients to have greater freedom over their aesthetic needs.

Vascular malformations, such as port-wine stains, and hemangiomas are commonly managed by facial plastic surgeons for cosmetic reasons.¹⁸⁰ The key to treating vascular malformations and hemangiomas is selective destruction of the pathologic vasculature, while minimizing injury to surrounding normal tissues. A secondary challenge is protecting against absorption of light by epidermal melanin, which has an absorption profile similar to that of hemoglobin.¹⁸¹ Absorption of laser energy by epidermal melanin can result in undesired thermal injury and pigmentary changes.¹³ Currently, port-wine stains are best treated with lasers.^{182 - 186} The best results for port-wine stain treatment are achieved using a PDL with cryogen cooling.^{147 - 154 ,182} Photodynamic therapy (PDT)¹⁸⁷ and nonablative therapies^{188 - 192} are effective against hereditary hemorrhagic telangiectasia. There is some indication of interest in using fractional photothermolysis to treat vascular lesions.^{193 - 194}

Laser tattoo removal was first attempted with the CO₂ laser nearly 30 years ago, yielding mediocre results.^{195 - 196} Modern treatment is pinioned on the Q-switched Nd:YAG,^{197 - 198} Q-switched ruby,^{197 ,199 - 200} and alexandrite lasers.^{201 - 204} These technologies have since remained the standard for tattoo removal and are used in combination with cryogen spray cooling.^{205 - 206} Future directions of laser tattoo removal will center on finding optimal wavelengths for complete elimination of tattoos with multiple colors.²⁰⁵

In 1996, Grossman et al²⁰⁷ published the first report of laser hair removal by selective photothermolysis of hair follicles using a normal-mode ruby laser. As with other laser therapies, novel laser sources were soon introduced, including the Nd:YAG laser,²⁰⁸ the alexandrite laser,²⁰⁹ and the diode laser.²¹⁰ Although laser hair removal typically entails multiple treatments to achieve desired results,^{211 - 212} patient satisfaction for laser hair removal is generally high.^{213 - 214} The main disadvantage of laser hair removal is the requirement for a considerable melanin gradient between skin and hair follicles.²¹⁵ As such, laser hair removal works optimally on patients with dark (high melanin content) hair and fair (low melanin content) skin, a condition that enhances the selective targeting of hair follicles, while sparing the skin. One active area of laser hair removal research concentrates on extending eligibility for laser hair removal to patients with light hair: Sadick and Laughlin²¹⁶ reported the use of combined intense pulsed light and RF energy in place of standard lasers for successful removal of white and blond hair, while Sand et al²¹⁷ attempted to supplement melanin before laser treatment using a liposome spray. Future laser hair removal studies will continue addressing the problem of removing light hair and will also seek solutions for emerging issues such as pain control, pediatric use, and paradoxical regrowth of hair after treatment.²¹⁸ Ultimately, laser hair removal devices will evolve to be portable and safe for home use.

Although standard surgical liposuction is generally safe and has been reported to have a very low complication rate,²¹⁹ it is limited to relatively large lobules of fat. The use of lasers in fat ablation would permit lipolysis on a mesoscopic scale, which is more suitable for use in the face. The first reported instance of laser fat ablation was via CO₂ laser.²²⁰ The technique became known as laser lipolysis and has since moved to the use of Nd:YAG and diode lasers as primary light sources. At the 2006 American Society for Laser Medicine and Surgery meeting, Anderson et al²²¹ discussed future laser lipolysis devices that can target a wide variety of fat, including sebaceous glands in acne, cellulite, xanthelasma, and fatty atheromatous plaques.

Laser lipolysis was shown to be safe and minimally invasive (requiring only a small incision), while causing desired skin retraction.^{222 - 224} Furthermore, laser lipolysis caused thermal damage in the fat that led to better hemostasis and wound healing, less surgical trauma, and faster recovery compared with traditional surgical liposuction.²²⁵ Traditional surgical liposuction can also be used safely with laser lipolysis.²²⁶ However, one study by Prado et al²²⁷ revealed high levels of fatty acid release into the bloodstream after laser lipolysis, underscoring the necessity of devising clearance mechanisms. As part of the trend of moving toward quantification of optical parameters, technologies today are capable of using mathematical models to help accurately estimate the magnitude of long-term fat-volume reduction and skin tightening after laser lipolysis.²²⁸

Photodynamic therapy is a multistep treatment involving targeted delivery and selective uptake of a photosensitive agent (earliest choice was 5-aminolevulinic acid²²⁹ ) in a desired site, optical activation of the photosensitive agent, and subsequent conversion of local tissue oxygen into tissue-killing reactive oxygen species.²³⁰ It was originally intended to have broad therapeutic value in medicine, primarily aimed at cancer therapy, and it has been used for the treatment of acne,^{231 - 232} rosacea,^{233 - 234} sebaceous gland hyperplasia,²³⁵ Bowen disease,²³⁶ basal cell carcinoma,^{229 ,237} and actinic keratosis.^{229 ,238} More recently, PDT has been used to rejuvenate the skin^{164 ,229 ,239 - 246} and is most popularly marketed in the form of a topical agent (Levulan Kerastick; Dusa Pharmaceuticals, Wilmington, Massachusetts). Current PDT research largely revolves around the development of combination photochemical and photothermal therapies such as PDT and RF,²³⁹ PDT and intense pulsed light,^{240 - 242} PDT and PDL,^{184 - 185 ,235 ,241} and PDT and blue light²⁴¹ for the purpose of photorejuvenation. Future challenges of PDT include identifying new, applicable photosensitive agents, identifying less costly light sources,²⁴³ and control of the pain (which is directly proportional to the number of treatments) associated with the therapy.²⁴⁷

At present, cutaneous laser therapy relies on the surgeon selecting dosimetry parameters based on the physical appearance of the targeted lesion as seen by the naked eye. This approach, while effective, is empirical and depends on clinical judgment, neglecting the consideration of several factors, such as the distribution of chromophores and the depth of the lesion within the tissue. Optimized dosimetry requires knowledge of the structural organization and cellular and molecular composition of the target. In vivo microscopy and related imaging technologies would allow intelligent treatment planning and design, as this structural and compositional information can be combined with numerical models of laser therapy to simulate results and optimize therapy. Obtaining lesion information before surgery and using this information to guide therapy represent an extremely active area of basic research. Verkruysse et al²⁴⁸ refer to this individualized therapy as “individual maximum safe radiant exposure,” a concept that should become the standard of future medical laser use.

Quantifying epidermal melanin content is an important task that would profoundly aid in the optimization of laser therapy for dark-skinned individuals, as results in these patients can be unpredictable. Currently, the measurement of epidermal melanin concentration and distribution is challenging.²⁴⁹ For example, commercially available melanin meters cannot distinguish between deoxyhemoglobin and melanin, indicating the need for devices capable of better separating the spectra of the 2 chromophores.¹⁸¹

Visualization of the deeper layers of the skin is another important process that would be instrumental in the optimization of laser cutaneous therapies. Several emerging in vivo imaging and microscopy technologies have been developed and may be potentially valuable in studying the skin. These cutting-edge modalities include (1) optical coherence tomography,^{250 - 257} (2) confocal microscopy,^{258 - 266} (3) multiphoton microscopy,^{257 ,267 - 274} (4) second harmonic generation imaging,^{267 - 268 ,271 - 275} (5) high-frequency ultrasonography,^{276 - 277} (6) photoacoustic imaging,^{278 - 283} and (7) modulated imaging.²⁸⁴ All of these technologies have resolution approaching that of conventional histopathology, but they can be performed in vivo without biopsy, fixation, and thin sectioning of the tissue. As computed tomography, magnetic resonance imaging, and ultrasonography have evolved over the past 20 years to diagnose tumors, to guide “macroscopic” surgery, and to monitor progression or improvement of disease, these microscopic imaging techniques may play a similar role in managing diseases of the skin and, accordingly, in optimizing aesthetic cutaneous procedures as well. Each of these technologies relies on specific optical properties of the tissue for image contrast. Multiphoton microscopy and second harmonic generation imaging are extremely intriguing as they resolve differences in tissue oxidation state or molecular structure (eg, collagen and elastin), respectively.

Ultimately, the gradual interest in using imaging and other diagnostic techniques to guide therapy will result in the refinement of dosimetry and better selective irradiation of targets within the skin. The use of such systems aims to create unique therapies that are safe, exact, predictable, and user friendly.

One of the most exciting developments for the future of medicine is the use of nanoparticles for targeted therapy. Research on this topic has largely concentrated on the use of gold nanoshells and nanoparticles, which can be designed to absorb light within a specified wavelength range.²⁸⁵ For medical purposes, the near-infrared range (800-1200 nm) is an ideal target because very few physiological chromophores absorb light in that region and, hence, light can penetrate deeply.²⁸⁵ Transfer of laser energy of that wavelength will therefore selectively heat only the nanoparticles and their surrounding structures. Moreover, nanoparticles exhibit nonlinear optical properties that depend on their size and dimension, allowing users to vary the optical properties of the constructs by changing their structural configuration, leading to infinite applications.²⁸⁵

Nanoparticles can be instrumental in enhancing drug delivery systems.^{286 - 287} This has great promise in coordinated drug delivery, as the time course and dosage of drug can be controlled by the application time and fluence of optical treatment, respectively. Nanoparticles can also be used for selective cellular ablation. This type of use has been demonstrated in vitro^{288 - 293} and in animal studies.^{294 - 295} In this capacity, nanoparticles have also been proposed for the treatment of port-wine stains²⁹⁶ owing to their effectiveness in targeting vasculature.²⁹⁷ More recently, studies have shown that tumor ablation is independent of location of nanoparticle entry: nanoparticles injected both intravenously or directly into the tumor site resulted in selective ablation after photothermal heating.²⁹⁸ Finally, nanoparticles can be used as a direct imaging modality^{285 ,287 ,291} or to increase contrast in imaging modalities such as optoacoustic imaging^{287 ,299 - 300} and optical coherence tomography,^{295 ,301 - 304} creating a high-resolution visualization of deep structures. Ongoing research in the field of nanoparticles will undoubtedly lead to identifying relevant applications to facial plastic surgery, such as its potential use to selectively target dermal collagen for rejuvenation. However, little is known of nanoparticle toxicity, particularly clearance.^{305 - 307}

The potential of spectroscopy as a high-resolution visualization and diagnostic tool in medicine is rapidly being realized. Spectroscopy relies on the optical excitation of tissues to acquire “molecular fingerprints” that are uniquely characteristic for a given molecule. When used on live tissue, which is heterogeneous, spectroscopy can provide detailed information on the tissue's molecular structural composition and can be used to distinguish among various disease states, the most important being cancers. Recent applications of spectroscopy include (1) reflectance spectroscopy for determining skin response to trauma^{308 - 309} and individual skin properties^{310 - 313} ; (2) fluorescence spectroscopy for quantifying skin aging³¹⁴ and early detection of skin cancer^{315 - 318} ; and (3) Raman spectroscopy for early detection of malignant neoplasms and cancers (eg, of the skin,³¹⁹ breast,^{320 - 322} colon,³²³ cervix,^{324 - 326} pancreas,³²⁷ and stomach³²⁸ ). In the future, spectroscopy will become more adapted for use in the clinical setting, eventually becoming an integral adjunct to in vivo noninvasive imaging modalities.

Low-level laser therapy (LLLT) involves the use of low-wavelength lasers (500-1000 nm) at low fluence rates to effect “biostimulation” of tissue via nonclassic pathways. Currently, LLLT has shown some promise in promoting wound healing,^{329 - 332} but this is debatable.^{333 - 334} There is also evidence that LLLT may have potential in influencing skin pigmentation.^{335 - 336} However, in vivo human skin studies and a thorough understanding of the wound healing response are necessary to confirm the true value of LLLT.

Congenital malformations or traumatic injury to cartilage can result in deformities that require surgical correction. Helidonis et al³³⁷ attempted the first case of laser cartilage reshaping in rabbit auricular cartilage as an alternative to surgical cartilage reshaping. Notable landmarks in laser cartilage reshaping research in the last decade include correcting nasal septal deviations,³³⁸ otoplasty,³³⁹ and testing the long-term in vivo viability of reshaped cartilage grafts.³⁴⁰ Finding the ideal optical medium and ensuring the viability of reshaped cartilage grafts will be extremely important in the future of this field.^{341 - 346}

Lasers and optical technologies have great value in facial plastic surgery. While they currently have significant roles in rejuvenation, hair removal, and fat ablation, lasers and optical technologies are becoming increasingly important for noninvasive imaging and targeted individualized therapy. Treatment of complex lesions such as port-wine stains will become more sophisticated as high-resolution imaging modalities and the wound healing response are studied more extensively. The growing interest in therapies that take individualized maximum safe radiant exposure into consideration will increase the treatments' individuality, safety, accuracy, and ease. This further refinement of lasers and optical technologies, which has been made possible in the last decade, will lead to the “smart” therapies of the next, expanding a truly promising subfield of facial plastic surgery for the benefit of both patients and physicians.

Correspondence: Brian J. F. Wong, MD, PhD, Beckman Laser Institute and Medical Clinic, University of California, Irvine, 1002 Health Sciences Rd E, Irvine, CA 92612 (bjwong@uci.edu).

Accepted for Publication: August 6, 2008.

Author Contributions:Study concept and design: Wu and Wong. Drafting of the manuscript: Wu and Wong. Critical revision of the manuscript for important intellectual content: Wu and Wong. Study supervision: Wu and Wong.

Financial Disclosure: None reported.

Additional Contributions: Bernard Choi, PhD, David Cuccia, PhD, Anthony Durkin, PhD, Lars Svaasand, PhD, and Wim Verkruysse, PhD, provided stimulating discussions and ideas, and Amanda Lim and Vanessa Rothholtz, MD, provided advice, commentary, and editorial assistance.