What is a laser?
LASERs (light amplification by stimulated emission of radiation) are sources of high-intensity monochromatic (single wave length) coherent light that can be used for the treatment of various dermatologic conditions depending on the wavelength, pulse characteristics, and fluence (energy output) of the laser being used and the nature of the condition being treated.
Various kinds of lasers are available; they are differentiated by the medium that produces the laser beam. Each of the different types of lasers has a specific range of utility, depending on its wavelength and penetration.
What is a pulsed dye laser?
- A dye laser is a laser which uses an organic dye mixed in a solvent as the lasing medium.
- Some of the laser dyes include rhodamine, fluorescein, coumarin, stilbene, umbelliferone, tetracene and malachite green.
- Some of the solvents used include water, glycol, ethanol, methanol, hexane, cyclohexane and cyclodextrin.
- A high energy source of light such as a fast discharge flashlamp or an external laser (eg, ruby laser or ND:YAG laser) is needed to "pump" the liquid beyond its lasing threshold.
- The dye solution is usually circulated at high speeds, to help avoid triplet absorption and to decrease degradation of the dye.
- The incoming light excites the dye molecules into the state of being ready to emit stimulated radiation.
- Pulsed dye lasers produce pulses of visible light at a wavelength of 585 or 595 nm with pulse durations of the order of 0.45–40 ms.
- Pulsed dye laser treatment can be combined with radiofrequency to enhance effects; lower PDL doses possible with the combination can reduce adverse effects.
How does the pulsed dye laser work?
- The pulsed dye laser, when used for dermatological applications, works on the principle of selective thermolysis.
- The selected wavelength of laser light is absorbed to a high degree by the target structure (called chromophores) compared to surrounding tissue.
- The pulse duration of laser energy is shorter than the target structure’s thermal relaxation time, which is the time taken for the target to cool by 50% of its peak temperature after irradiation.
- This ensures that the impact of thermal energy is limited to the target structure and does not affect the surrounding tissue.
- When pulsed dye laser light hits the skin, it is reflected, transmitted, or absorbed.
- Absorbed energy is most responsible for the clinical effect because it is converted to thermal energy (heat) by the intended targets (chromophores), thereby killing the diseased cells.
- The skin chromophores commonly targeted by the pulsed dye laser is haemoglobin in blood.
- Complications result when energy intended for the target chromophore is non-selectively diffused and absorbed by surrounding tissues and structures.
What is a pulsed dye laser used for?
The following skin disorders may be treated with pulsed dye laser (PDL) beams using an US Federal Drug Agency (FDA)-approved machine such as Vbeam Perfecta® (Candela Corporation, Massachusetts, USA) or flashlamp pulsed dye laser (Cynosure VLS, Massachusetts, USA).
Cutaneous vascular lesions
- PDL is useful in the treatment of port wine stains (vascular malformation), superficial haemangiomas and a variety of acquired cutaneous vascular lesions, including telangiectasis, cherry angiomas and poikiloderma of Civatte.
- Light energy emitted by the flashlamp-pumped PDL is primarily absorbed by oxyhemoglobin contained within blood vessels, thus minimising thermal damage to other structures.
- Laser treatment parameters are based on several factors, including lesion location, lesion morphology, and patient skin type.
- Spot sizes ranging from 2–10 mm are used to deliver a fluence averaging 5–10 J/cm2.
- The use of larger spot sizes and a higher fluence permits deeper dermal penetration and destruction of larger blood vessels.
- Lower energy densities are necessary in anatomic locations with an increased risk of scarring, such as the anterior chest, neck, and periorbital area.
- The physician should apply laser pulses in a nonoverlapping manner to prevent excessive thermal damage (burns) that could result in blistering and scarring.
- Port-wine stains treated with the pulse dye laser and a cryogen-cooling device have been shown to have a significantly better response at 585 nm than at 595 nm.
- In general, port-wine stains fade by 80% after 8–10 treatments. Lesions on the face or neck tend to respond more quickly than those on the lower extremities.
- For the treatment of port-wine stains, hemangiomas, and facial telangiectasias, the 585 nm pulse dye laser has the best clinical track record for both effectiveness and safety, regardless of patient skin phototype.
Non-vascular skin conditions
- PDL is also widely used to treat several nonvascular conditions including plane warts, angiofibroma (tuberous sclerosis) and pyogenic granulomas.
- PDL has been shown to be beneficial for these conditions in fair-skinned (Fitzpatrick skin types I–III) individuals.
- The procedure is repeated at intervals of 4-6 weeks up to an average of 3 sessions.
The laser parameters used are:
- Plane warts: spot size 5 mm, fluence 5.5–7.5 J/cm2, wavelength 585 nm, pulse duration 0.45 ms (single pulse per lesion)
- Angiofibroma: spot size 5 mm, fluence 6–8.5 J/cm2, wavelength 585 nm, pulse duration 0.45 ms (2 pulses per lesion)
- Pyogenic granuloma: spot size 5 mm, fluence 7 J/cm2, wavelength 585 and 595 nm alternately, pulse duration 1.5 ms (4–5 pulses per lesion).
- Melasma is an acquired pigmentary disorder characterised by brownish hyperpigmented patches usually on the face.
- The role of pulse dye laser in melasma treatment is controversial with studies showing conflicting results.
- At least one study has shown that 3 sessions at 3-week intervals with fluence up to 10 J/cm2 and pulse duration up to 20 ms is effective in the treatment of patients with melasma.
Burn and hypertrophic scars
- The 585 nm PDL has emerged as a successful alternative to excision in patients with hypertrophic scars following thermal burns.
- Multiple studies have shown the PDL's ability to decrease the redness and thickness of a scar, while significantly decreasing itch and improving the cosmetic appearance of the scar.
Nail psoriasis/plaque psoriasis
- Several studies have proven the efficacy of PDL in the treatment of plaque psoriasis. Two published studies indicate PDL may be effective on nail psoriasis.
- Biological agents are probably more effective, however.
What does the laser procedure involve?
It is important that the correct diagnosis has been made by the clinician prior to treatment with PDL laser, particularly when pigmented lesions are targeted, to avoid mistreatment of skin cancer such as melanoma. The patient should wear eye protection, consisting of an opaque covering or goggles, throughout treatment.
- Treatment with the PDL laser consists of placing a hand piece against the surface of the skin and activating the laser. Many patients describe each pulse to feel like the snapping of a rubber band against the skin.
- Topical anaesthetic may be applied to the area, but is not usually necessary.
- Skin surface cooling is applied during all hair-removal procedures. Some lasers have built-in cooling devices.
- Immediately following treatment, an ice pack may be applied to soothe the treated area.
- Care should be taken in the first few days following treatment to avoid scrubbing the area, and/or use of abrasive skin cleansers.
- A bandage or patch may help to prevent abrasion of the treated area.
- During the course of treatment patients should protect the area from sun exposure to reduce the risk of postinflammatory pigmentation.
- After treatment, loose clothing should be worn to avoid rubbing, the treated area should not exposed. Swimming, saunas, hot baths and contact sports should be avoided until the treated area is healed.
Are there any side effects from pulsed dye laser treatment?
Side effects from pulse dye laser treatment are usually minor and may include:
- Pain during treatment (reduced by contact cooling and if necessary, topical anaesthetic)
- Redness, swelling and itching immediately after the procedure that may last a few days after treatment.
- Rarely, skin pigment may absorb too much light energy and blistering can occur (a burn). These symptoms recover.
- Changes in skin pigmentation. Sometimes the pigment cells (melanocytes) can be damaged leaving darker (hyperpigmentation) or paler (hypopigmentation) patches of skin. Generally, cosmetic lasers will work better on people with lighter than darker skin tones.
- Bruising (purpura) affects up to 10% of patients. It usually fades on its own.
- Bacterial infection. Antibiotics may be prescribed to treat or to prevent wound infection.