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May/June 2014 Today's Veterinary Practice 63 Laser Therapy in Companion Animals REVOVERY & REHAB | tvpjournal.com Further, in-depth discussion of bio- chemical reactions is beyond this arti- cle's scope. Osteoarthritis The anti-inflammatory effects of laser therapy are considered to be due to reduced levels of PGE2 and COX-2. 10 In rat osteoarthritis (OA) models, laser therapy (1) reduced edema within the joint by 23%, (2) decreased vascular per- meability in the periarticular tissue by 24%, and (3) decreased pain by 59%. 11 Some subjective studies in humans with OA have shown (1) improved quality of life, 2 (2) reduced pain, and (3) increased analgesic and microcircula- tory effects. 12 However, there have been conflicting reports in human medicine that reveal no benefits of laser therapy. 1 Therefore, it has been suggested that individual results may depend on: • Type and extent of disease • Wavelength • Method of application • Dosage • Site • Duration of treatment. Tendon & Ligament Conditions An experimental study in rats with cal- caneal lesions treated with laser therapy revealed improved collagen organiza- tion in the treatment group compared with the control group, with 5-day treat- ment providing optimal response. 13 In humans, results are conflicted, with about 50% of studies showing a positive effect and 50% showing no effect. In human ligamentous injuries, laser therapy has shown improved tensile strength and stiffness com- pared with controls. 14 Pain Management The exact mechanisms remain un- known, but it is thought that laser therapy has the potential to influence pain perception by direct and indirect actions on superficial nociceptors and modulation of inflammation. Further- more, repeated application of laser therapy may decrease central sensitization. Laser effects appear to be mainly inhibitory for pain receptors, and sensory nerves are more commonly affected. 1 The superficial location of A delta and C nerve fibers, along with neurons that supply the vasculature for vasoconstriction and vasodilation, allows laser penetration. Unfortunately, use of lasers for pain Figure 2. An example of a Class 3 laser. Courtesy ruby Lynn Carter, LvT, CCrT, Mississippi State University LASER CLASSIfICATION Laser classification is based on wavelength and maximum output in power or energy. Current classifications consist of class 1 through 4. Class 1 lasers are very mild and safe. They include lasers used in everyday life; for example, those used in equipment that implements bar code scanning, such as cash registers at the supermarket. Class 2 lasers are in the visible light spectrum (400–700 nm). Some therapeutic lasers and laser pointers fall into this class. Damage can occur if the laser is directed into the eye for prolonged periods. Class 3 lasers (figure 2) include the commonly used therapeutic lasers. These lasers are further subdivided into: • Class 3B lasers are either continuous in the visible to infrared spectrum, or pulsed in the visible light spectrum. • Class 3R lasers are continuous within the visible light spectrum and have less power than Class 3B lasers. Class 4 lasers are the strongest lasers, and mostly include surgical lasers. They have the ability to permanently damage the eyes or burn the skin. KEY RECOMMENDATIONS » With Class 3 lasers (3B and 3R), eye protection must be used at all times (figures 3 and 4). » With Class 4 lasers, eye protection must be worn and the clinician must use great care to control the beam. 1 Figures 3 and 4. Eye protection should always be worn when the laser is in use; this includes any individuals in the room as well as the patients, if they will tolerate it. Courtesy Artise Stewart, dvM, CCrP, Charleston veterinary referral Center, Charleston, SC TVP_2014_0506_RecovRehab_LaserTherapy.indd 63 5/23/2014 6:02:11 PM