Introduction

A variety of technologies purported to improve tissue healing or to reduce inflammation are available to the practitioners. There is considerable growth in the use of therapeutic laser in the multimodal management of the patients. The effects of laser protocols remain incompletely understood. Nevertheless, a considerable body of scientific evidence on the possible physiological mechanisms underlying such treatment is available. Such information should guide the indications and protocols for the use of therapeutic laser in practice.

Laser is an acronym for Light Amplification by Stimulated Emission of Radiation. Light by definition is electromagnetic radiation which consists of both a waveform and of particles. Therapeutic laser or low-level light therapy, meaning the application of light energy in the red or near infrared spectrum to tissues, has been extensively studied. Instead, photobiomodulation better describes the medical interactions produced by the diversity of lasers currently available. The terminology employed in laser instrumentation is derived from these characteristics:

• Photons: Energy transmitted via light
• Wavelength: Determines color and classification of light energy; measured in nanometers (nm)
• Sunlight contains electromagnetic radiation with wavelengths between approximately 100 nm and 1 mm. This is further subdivided into ultraviolet light (<400 nm), visible light (400–700 nm), and infrared (700 nm to 1 mm).
• Wavelength is the critical variable in determining laser penetration and tissue absorption.
• Hemoglobin and melanin are known to absorb energy (photons) at wavelengths less than 600 nm. The absorbance of water increases at wavelengths greater than 1000 nm. Therefore, ideal wavelengths for therapy are between 600 and 1000 nm, with shorter wavelengths used for superficial tissue and longer wavelengths used to penetrate deeper tissues.
• In general, wavelengths for specific conditions are as follows:
• 904/905 nm is better for pain
• 808–860 nm is better for inflammation
• 600–700nm is best for skin lesions and antimicrobial effects
• Spatial coherence: The degree to which light is focused in a beam
• Temporal coherence: The degree to which light has a single frequency
• The critical difference between sunlight and laser therapy is spatial and temporal coherence, meaning that light is focused at a particular wavelength on an intended spot. Therefore, the dose is narrowly applied to a therapeutic window as dictated by the properties of light interaction in a particular tissue.
• Irradiance: Power of laser divided by spot size; calculated as Power (W)/Area (cm2)
• Power density and light energy: Power is measured in Watts (W), which is defined as one joule per second (W= J/cm2). Light energy is measured in Joule (J). A joule is therefore a unit of energy required to produce one watt of power for one second (1 Joule = 1 Watt x 1 second).
• The total energy transferred to the tissue is reflected in J/cm², whereas the irradiance of a laser is expressed in W/ cm².
• A higher-powered laser can produce more energy per unit of time, which allows it to deliver laser energy faster, as well as to cover a larger treatment area by using a larger beam diameter.
• Power has absolutely nothing to do with depth of penetration, or targeting of specific tissues.
• The total dose of visible or infrared light in a human spending one hour outdoors would be about 180 J/cm².
• Current dosage recommendations
• Acute conditions, superficial wounds, or inflammatory conditions: 1–4 Joules/cm²
• Pain, chronic conditions, or deep-seated conditions: 6–10 Joules/cm²
• Deep-seated, chronic, or severe infections: 10–30 Joules/cm²
• A 3x5 card, an average man’s palm, or a CD is approximately 100 cm². A quarter is about 5 cm².An “Oreo” is about 25 cm².

Laser Classification

The laser classification system defines the amount of power emitted; class IIIa emits (1 to 5 mW output), class IIIb (5 to 500 mW output), and class IV (>500 mW output). Class IIIb lasers and Class IV lasers are the most commonly- encountered in veterinary practice. The efficacy of class IIIb and class IV laser therapy has been documented.^1-3 Current thought is that physiologic effects are seen with both high- and low-power settings.^2,3 Not all therapeutic lasers are created equal, so it is important for veterinarians to be educated about the science and safety of therapeutic laser application. Veterinarians must do your homework so to not be seduced by marketing materials, as well as be prepared to continue learning as new information about applications becomes available.

Is the Laser Really Doing Anything?

A therapeutic laser is used for three main purposes:

1.  To promote wound healing, tissue repair, and the prevention of tissue death

2.  To relieve inflammation and edema because of injuries or chronic diseases

3.  As an analgesic and a treatment for other neurological problems

These applications appear in a wide range of clinical settings, ranging from dentistry, to dermatology, to rheumatology and physiotherapy. The primary effects of photobiomodulation based on the current experimental literature include:

1.  Cellular effects

a.  Increase of adenosine triphosphate (ATP) production

b.  Increase of cell membrane pump function

c.  Increase of cell respiration

d.  Production of reactive oxygen species

e.  Reduces the production of substance P

f.  Stimulates long-term production of nitric oxide

g.  Decreases the formation of bradykinin, histamine, and acetylcholine

h.   Stimulates the production of endorphins

2.  Gross effects

a.  Analgesia

b.  Antiinflammatory

c.  Antiedema

d.  Circulation improvement

e.  Enhanced wound healing

f.  Enhanced healing of tendons and ligaments with superior tensile strength

g.  Nerve cell damage repair

h.  Increased collagen synthesis

i.  Slow or reversed tissue degeneration

Clinical Applications

Laser therapy has been found to offer superior healing and pain relieving effects compared to other electrotherapeutic modalities, especially in the early stages of acute injuries, and for chronic problems. Laser therapy can be used to treat muscle, tendon, ligament, connective tissue, bone and skin tissue, however, excellent results are also achieved when it is used to complement other treatment modalities, such as acupuncture, electrotherapy, therapeutic ultrasounds, and physical exercises. The current research on laser therapy in veterinary medicine is limited. A recent controlled trial showed improved ambulation times following intervertebral disc disease when laser therapy was used after surgery. Most studies, however, employ varying treatment doses and laser wavelengths.

Additional clinical trials with dose standardization are needed in veterinary medicine. Laser has been shown to be effective in, but not limited to, the treatment of the following indications:

780–830 nm Infra-Red Wavelengths - Deep Tissue Penetration

• Sprains and strains
• Wounds and abrasions
• Hematomas
• Ligament & tendon injuries, bowed tendon
• Inflammation (joints, ears, muscles)
• Joint injuries
• Myofascial trigger points, pain points and deep-tissue acupuncture points
• Chronic and acute pain
• Non-union and small-bone fractures
• Lick granulomas

630–700 nm Visible Red Wavelengths - Shallow Tissue Penetration

• Wounds and abrasions
• Superficial acupuncture points
• Mucous membranes
• Post-surgical wounds
• Inflammation (skin, wounds)

Laser therapy effects are cumulative: Response should improve with each treatment and/or duration of response should increase with each treatment until a plateau is reached or condition is resolved. Chronic injuries should be treated every other day initially. A good starting protocol could be 3 times week one, then twice the following week, then once a week later. Acute injuries can be treated 2–3 days in a row then follow to every other day and so on. As response is noted, lengthen the time between treatments gradually until condition is resolved or acceptable patient comfort is maintained. This is often achieved in 6–10 treatments on average. In severe or chronic conditions, treat at least weekly (twice weekly would be preferred) until resolved. Once to twice monthly intervals may be adequate for maintenance. Most patients will show at least a mild positive response in 1–2 treatments. If positive response is not noticed in 3–4 treatments with standard protocol, re-evaluate condition, treatment protocol or diagnosis.

Safety and Contraindications

Laser therapy has a wide margin of safety. The North American Association for Laser Therapy (NAALT) has compiled the following list of contraindications: pregnancy (over the pregnant uterus), cancers (over the tumor site), hemorrhagic areas, endocrine glands, pediatric joint epiphysis, transplant patients, or other immuno-suppressed patients, and photosensitive patients. Laser can damage optic tissue. Protective eyewear should always be worn by the clinician and the patient during treatment.

References

1.  Chung H, Dai T, Sharma SK, et al. The nuts and bolts of low-level laser (light) therapy. Annals of Biomedical Engineering 2012;40:516–533.

2.  Cristante AF, Damasceno ML, Barros Filho TEP, et al. Evaluation of the effects of hyperbaric oxygen therapy for spinal cord lesion in correlation with the moment of intervention 2012;50:502–506.

3.  Draper WE, Schubert TA, Clemmons RM, et al. Low-level laser therapy reduces time to ambulation in dogs after hemilaminectomy: a preliminary study. Journal of Small Animal Practice 2012;53:465–469.

4.  Prindeze NJ, Moffatt LT, Shupp JW. Mechanisms of action for light therapy: a review of molecular interactions. Experimental Biology and Medicine 2012;237:1241–1248.

5.  Woodruff LD, Bounkeo MS, Brannon WM, et al. The efficacy of laser therapy in wound repair: a meta-analysis of the literature. Photomedicine and Laser Surgery 2004;22:241–247.

6.  Tunér J, Hode L. The New Laser Therapy Handbook: A Guide for Research Scientists, Doctors, Dentists, Veterinarians and Other Interested Parties within the Medical Field. Grängesberg, Sweden: Prima Books, 2010.

7.  Hudson DE, Hudson DO, Wininger JM, Richardson BD.Penetration of laser light at 808nm and 980nm in bovine tissue samples. Photomed Laser Surg 31:163–168, 2013.

8.  Bjordal JM, Couppé C, Chow RT, et al. A systematic review of low level laser therapy with location specific doses for pain from chronic joint disorders. Aust J Physiother 49:107–116, 2003.

9.  Al-Watban FA, Zhang XY, Andres BL. Low-level laser therapy enhances wound healing in diabetic rats: A comparison of different lasers. Photomed Laser Surg 25:72–77, 2007.

10.  Viegas VN, Abreu ME, Viezzer C, et al. Effect of low level laser therapy on inflammation reactions during wound healing: Comparison with meloxicam. Photomed Laser Surg 25:467–473, 2007.