Phototherapy Unveiled: A Review of the Photobiological Basics Behind Athermal Photobiomodulation with Lasers and Other Light Sources. Part 1: Light - Its Properties and Parameters (original) (raw)

best only partly understood is the athermal reaction which accompanies with very few exceptions all photothermal reactions associated with the surgical laser. One particular field where this athermal reaction plays a role at least as important as the thermal reactions is in the application of nonablative light sources in the rejuvenation of photoaged skin. This field is expanding rapidly, but the photobiology behind the processes by which a particular type and dose of light can repair damage (which was actually also caused in the first place by light) is imperfectly understood. Although the main concept of nonablative skin rejuvenation is centred on the creation of a controlled zone of delivered thermal damage (DTD) in the upper dermis under a cooled epidermis, the incident light energy, in the form of photons, does not simply stop at the DTD zone but continues on into the surrounding dermal tissue, mediating athermal photoreactions in the periphery of that thermal effect. These athermal reactions, at a cellular and subcellular level, contribute a great deal to the modulation of the wound healing process instigated by the DTD to produce the final hoped-for results. This article examines the range of athermal photoreactions which occur simultaneously with the thermally-mediated effects in nonablative skin rejuvenation, to a great extent in laser ablative resurfacing and indeed in any surgical application of the laser, and attempts to show the importance of these photobioreactions in achieving good clinical results. This first part of the series may well appear as 'old hat' to experienced users of lasers and light sources, but we feel it is important to start from the basics, rather than having to return to them to try and discover why tissue has failed to react to the incident light in the expected manner, and a possibly unhappy patient as a result. A thorough understanding of the basic properties of light and its parameters is extremely important when trying to appreciate the complexities of light-tissue interaction. Without this understanding, moreover, no-one should be using any form of light source on patients.

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