Principles of laser and intense pulsed light for cutaneous lesions
- George J Hruza, MD
George J Hruza, MD
- Clinical Professor of Dermatology and Otolaryngology
- St. Louis University School of Medicine
When absorbed in sufficient amounts, light energy can induce changes in the skin. Lasers and intense pulsed light (IPL) devices allow for the delivery of light to the skin in a controlled manner. These devices are useful for achieving desired clinical effects in a variety of dermatologic conditions.
The term laser is an acronym for light amplification by stimulated emission of radiation. Lasers deliver monochromatic, coherent, collimated, high intensity beams of light. In contrast, IPL devices are filtered flashlamps that emit polychromatic, noncoherent light in a broad range of wavelengths. Thus, IPL devices are dimmer and less powerful than lasers.
For many years following the initial studies of the effects of lasers on the skin [1-4], the use of lasers was limited to nonselective coagulation and vaporization of tissue . A revolution in the clinical utility of lasers occurred in the early 1980s with the development of the theory of selective photothermolysis . This theory describes the parameters by which light can be used to selectively destroy targets in the skin through the selective absorption of light and spatial confinement of the effect. The majority of subsequent developments in laser technology for cutaneous disorders have been based upon this theory.
Progress in laser and IPL technology has also involved the development of safer and more efficient methods of achieving the desired effects on skin. Cooling technology limits inadvertent damage to tissues adjacent to targeted sites, allowing higher levels of light energy to be directed towards the target. In addition, the implementation of fractionated laser technology for cutaneous resurfacing has allowed for the achievement of the desired cosmetic outcome with reduced healing time.
The principles that govern the interactions between skin and laser light or IPL, and the types of these devices used in the treatment of skin will be discussed here. Background information on the production and basic characteristics of laser light, the treatment of cutaneous vascular and hyperpigmented lesions with laser light, and ablative laser resurfacing for skin rejuvenation are reviewed separately. (See "Basic principles of medical lasers" and "Laser and light therapy for cutaneous vascular lesions" and "Laser and light therapy for cutaneous hyperpigmentation" and "Ablative laser resurfacing for skin rejuvenation".)
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- SKIN OPTICS
- SELECTIVE PHOTOTHERMOLYSIS
- THERAPEUTIC PARAMETERS
- Pulse duration
- - Thermal relaxation time
- - Large versus small structures
- Spot size
- FRACTIONAL PHOTOTHERMOLYSIS
- SKIN COOLING
- CLASSIFICATION OF DEVICES
- Continuous and quasi-continuous wave lasers
- Pulsed lasers
- Fractionated lasers
- - Nonablative
- - Ablative
- Intense pulsed light
- OTHER LASER/LIGHT TISSUE INTERACTIONS
- Excimer laser
- Photodynamic therapy
- SUMMARY AND RECOMMENDATIONS