What is Laser Power and How Does it Affect Photobiomodulation (PBM)?
The laser light energy is measured by the laser power.
Power seems simple but simply stating the output power does not relate the whole story when discussing therapy laser treatment. Not only is power important, but also the size of the area that is being treated. Typical power units for a laser are watts (abbreviated as W). Power is a measure of the number of photons emitted from the laser each second. Early therapeutic lasers had very low powers (less than 0.5 W) and very small beam areas (or spot sizes); consequently, early studies were often disappointing because the low powers were not able to provide sufficient number of photons to reach deeper affected tissue.
The Food and Drug Administration (FDA) classifies laser according their output power and recognizes four major classes (I to IV) of lasers, including three subclasses (IIa, IIIa, and IIIb).In December 2003, the FDA approved the first Class IV laser for the relief of minor muscle and joint pain.In October 2006, LiteCure was formed and FDA approval for the LCT-1000 a Class IV therapy laser was granted in February, 2007. LiteCure lasers are class IV lasers; they have an output power that is greater than 0.5 W.
Because Class IV lasers have a higher output power, there are some additional safety considerations that should be followed when using a Class IV laser. Eye safety is the most important consideration and the laser light should not be directed into an eye. The practitioner and patient should wear approved safety glasses for further protect from inadvertent beam reflections.
It is important to note that the LiteCure lasers not only have higher power but also have a larger beam area, making them better capable of delivering therapeutic dose to larger treatment areas.
Why are Higher Powers Needed?
Simply stated the greater the number of photons delivered to the surface, the greater the number of photons at any tissue depth. There is a threshold, a minimum number of photons that are needed to “turn on” the therapeutic effects of laser light. Hundreds of scientific studies have been done in vitro and have characterized the dosages needed to achieve a cellular response with light. These studies provide a baseline for the amount of laser energy needed to achieve results at the cellular level. PBM therapy is non-invasive; the light is applied to the surface of the skin. Some of that light is reflected by the skin or absorbed by other chromophores that are not associated with the injured cells and therefore do not contribute to PBM. Sufficient dose needs to be applied to the skin so that despite these losses sufficient dose reaches the skin and PBM occurs at the target tissue.
The figure to the left illustrates ,with infrared images, the amount of light seen on the back of the hand when laser light is applied to the palm at 1 watt, 5 watts, and 10 watts of power.
The greater the power, the greater the penetration to deeper tissue for a given amount of time. With the higher powered lasers, it is possible to not only apply the benefits of PBM superficially, but it is also possible to treat a greatly expanded range of conditions by delivering a clinically effective quantity of photons to cells deep within the tissue.
