Aesthetic lasers target chromophores: water, melanin, oxyhemaglobin, and exongenous chromophores such as carbon-based ink found in tattoos.¹ Lasers produce monochromatic light and are named by the specific wavelength they produce. Due to this nature no laser can supply all the wavelengths needed for different targets.

Understanding light interactions with skin is essential to appropriately treating and achieving results as well as knowing laser and light-based wavelengths, fluences, and pulse durations. There are numerous energy-delivering devices, light-based devices and lasers on the market currently. Fully understanding how they work and what target they work best on is essential to incorporating them into patient care.

IPL therapy can be used to effectively treat vascular and pigmented lesions that may be seen in photodamaged skin and is also used to reduce unwanted hair. IPL is discussed extensively in Chapter 22. The reader is invited to review the relevant sections.

Non-ablative laser therapies treat the target chromophores of water, melanin, and oxyhemaglobin and leave the surrounding skin intact. As the stratum corneum remains intact, the skin maintains its defense function to microbial infection and highly minimizes the risk of potential side effects as compared to ablative techniques. Due to the nature of treatment there is less downtime and less risk of infection versus ablative laser therapies. Lasers falling below the infrared range of 2,000 nm are non-ablative.³

Ablative lasers such as the CO₂ 10,600 nm or the Erbium:YAG 2,940 nm ablate the target chromophore as well as vaporize surrounding tissue and have significant downtime typically ranging from three to ten days if fractionated and 7 to 14 days if unfractionated. Due to corneum stratum breakdown there is a higher risk of infection as the skin’s defense system is open.⁴ High risk yields high reward though as these treatments can produce significant results. More discussion on ablative technology will be made in Chapter 24.

Fractional laser treatments introduced by Anderson and Parrish utilize fractional photothermolysis to generate microthermal zones.⁵ This means that the energy is delivered in columns rather than complete ablation. When this technology is utilized it creates micro-wounds in the skin surrounded by intact tissue. This heating, up to mid-reticular dermis, serves as the stimulus for inflammatory mediator release, fibroblast activation, neocollagenesis, and dermal remodeling. Furthermore, the impacted coagulation columns act like elimination channels, which expel pigment and explain the clinical lightening of lentigines and melasma.⁵

When delivered this way it allows deeper penetration into the tissue without compromising more superficial tissues. Typically, multiple treatments are required to achieve best results, but there is less downtime, an average of three days, associated with each treatment (Fig. 23.2). Fractional technology can be found in both ablative and non-ablative lasers.²

Q-switched means that instead of the laser operating in a continuous wave (CW) it stores energy and is able to produce an increased pulse or higher pulse energy and longer pulse duration. This also allows the laser to shatter pigment including those
in tattoos and pigmented lesions that can then be absorbed by phagocytosis and expelled through the lymphatic system (Fig. 23.3).²

Picosecond lasers entered the market specifically for tattoo removal as they pulse at a picosecond versus a nanosecond (Fig. 23.4).⁶ They have expanded capabilities, but since tattoo removal doesn’t typically take place in the periorbital area the discussion about picosecond lasers will be limited here.

RF technology is used for bulk heating of tissue and is primarily used for skin tightening and collagen remodeling (Figs. 23.5, 23.6, 23.7). Water is the only chromophore it targets making the device “colorblind,” therefore it can be used on any skin type. Elevation of dermal layer temperature leads to a transient denaturation of structural collagen fibrils, which is followed by contraction and tightening of the skin. Heat is applied to the epidermis creating an inflammatory phase that last one to three days. Early contraction of blood vessels during the initial heat of 39°C to 42°C is followed by vasodilation in order to increase blood supply, which can last multiple hours to one to three days. Macrophages, neutrophils, and other cells infiltrate the damaged area to remove dead/damaged tissue and destroy bacteria. The proliferative phase will last up to three weeks in which there is an ongoing process to repair tissue. During days two to three there is fibroblast activity that is induced in damaged tissue. Fibroblasts multiply, sending mediators to stimulate repair, combining with damaged tissue. Fibroblasts will begin collagen synthesis usually around day 7 up to day 21. Old collagen is removed by collagenase during this time as well. The maturation phase starts at week three
and will continue for six months and sometimes beyond where new collagen is generated and elastin becomes more uniform and its quality is improved.⁷ Typically 2 to 4 treatments performed four weeks apart are generally needed to see a clinically measurable response.⁷ There are multiple studies in the literature on the effectiveness of RF technology in the periorbital region.⁷ The author introduces the technology here as it
is a noninvasive option with no downtime to rejuvenate skin and can be used in conjunction with other treatment modalities being discussed to attain a synergistic effect.

Selective photothermolysis is the mechanism of action of laser therapy as it targets chromophores melanin, oxyhemaglobin, and water. Photons of light produced by the laser are absorbed by the specific chromophore within a specific target, producing heat. The heat dissipates and when sufficient energy is delivered faster than the rate of cooling, heat accumulates within the target and selectively destroys it. Tissue absorption and scattering determine penetration of laser light into the skin. Longer
wavelengths can penetrate deeper into the skin, but as the wavelength is increased into the far-infrared region, light is heavily absorbed by water, which limits its penetration.⁵ Since soft tissue is an organic composite mainly composed of water and structural proteins, it is very helpful to know laser absorption and tissue penetration by wavelength. Wavelengths or “color” of light in the infrared range (2,000 nm and above) are ablative in nature due to the absorption of water and limited penetration.⁵ It is also imperative to understand that thermal relaxation time (TRT), which largely determines the ideal pulse duration for selective thermolysis, in seconds is directly proportional to the square of the target size in millimeters. For example, a 0.2-mm telangiectasia, typical for rosacea, cools in about 0.04 seconds (40 ms). The optimal laser or IPL pulse duration is typically approximately equal to the TRT, so in this example a pulsed dye (595 nm) laser operated at ˜20 to 40 ms would be appropriate.¹

The following list of lasers may not be all-inclusive as the market is increasing at a fairly rapid rate and is meant to serve as a guide and introduce familiarity to wavelengths and target chromophores (Fig. 23.8).

CO₂ lasers 10,600 nm: This is a gas laser in the mid infra-red spectrum that is highly absorbed in water. It is hypothesized that CO₂ lasers cause immediate contraction of the ablated areas by denaturing existing old collagen.¹,⁶ This laser is ablative and will be discussed in more detail in Chapter 24.

Erbium 2,940 nm: This is a solid-state laser that is highly absorbed in water and is used for laser resurfacing and skin rejuvenation. This frequency is much closer to the peak absorption range of water and thus has an absorption coefficient 16 times greater than the CO₂ laser. This greater absorption decreases the penetration depth into the epidermis by a factor of 10. This is an advantage, as more precise ablation of skin is possible with even less damage to surrounding tissue.¹,⁶ This laser is ablative and will be discussed in more depth in Chapter 24.

1,540 to 1,565 nm: These lasers are considerably less absorbed by intracellular water than the ablative 10,600 nm CO₂ and the 2,940 nm Erbium:YAG lasers, making them non-ablative. They are typically used for skin resurfacing procedures including periorbital wrinkles.⁸

Nd:YAG 1,064 nm: This is absorbed by many chromophores. It is highly absorbed in hemoglobin so it works well for the treatment of vascular conditions. Melanin absorbs this wavelength and it is useful for hair removal and tattoo pigment.¹,⁶ Alexandrite 755 nm: This laser is highly absorbed by melanin, and it is considered by some to be the gold standard for hair reduction with those that have light skin and dark hair.¹,⁶

Pulsed dye 577 to 585 nm: These lasers are absorbed by hemoglobin so they are used in vascular treatments and vascular staining such as port wine stains.¹,⁶