Laser therapy is a treatment modality that has been utilized for decades, but is finally finding its place in mainstream veterinary medicine. Interest in the application of therapeutic laser for the treatment of various conditions has grown dramatically as anecdotal reports, clinical case reports, and systematic study results have become available. Therapeutic laser has been incorporated into treatments that address diverse conditions including:
- Skin wounds
- Tendon and ligament injuries
- Trigger points
- Lick granulomas
- Muscle injuries
- Nervous system injury and neurologic conditions
- Post-operative incisions and tissues
In order to understand how to best leverage therapeutic laser for appropriate treatment applications, it is important to understand the basics of laser technology, whether using therapeutic laser as a standalone modality or as a part of a larger treatment protocol.
The term “laser” is an acronym that stands for “light amplification by stimulated emission of radiation”, and describes a device that emits radiation in the form of a flow of photons of light energy. Therapeutic laser has been referred to as “low level” laser and “cold” laser, but these are considered obsolete terms. They were intended to distinguish therapy lasers from surgical lasers. Surgical lasers rely on different media – gas or solid – to incise or ablate tissues as an alternative to using a scalpel or cautery, respectively.
Therapeutic lasers help modulate cellular functions through a process called photobiomodulation, a photochemical process in which photons from a laser source interact with the target cells via a non-thermal mechanism to cause either stimulation or inhibition of biochemical pathways. While the precise mechanism for photobiomodulation is not completely understood, it appears that cytochrome C, located in the mitochondria, serves as an important photoreceptor. Once light is absorbed by cytochrome C, mitochondrial respiration and ATP production increase, leading to global tissue effects.
Laser light is monochromatic (one wavelength), coherent (all photons travel in the same phase and direction), and collimated (minimal divergence of the laser beam over a distance). These three properties allow the therapy laser light to be focused on a specific area of the body, to penetrate the skin without heating or damaging it, and to interact with tissue with few side effects. The beam should be aimed at 90° to the surface of the area being treated. Wavelength influences the depth of penetration, and longer wavelengths penetrate deeper into the tissues. The optimal wavelength range for tissue photobiomodulation appears to be 650nm to 1,300nm; at longer wavelengths the laser beam penetrates deeper into tissue while minimizing absorption by the pet’s hair and skin pigment. Superficial wounds and joint injuries can be treated with shorter wavelengths, while longer wavelengths are better suited to treat muscle injuries.
The power of the therapeutic laser matters in terms of the dose delivered, and the time needed to deliver the treatment dose. Power is a unit of time, and is expressed in watts (W) or milliwatts (mW). One watt is one Joule of energy delivered per second, and the laser dose is typically expressed as Joules/cm2 – the energy delivered over a surface area. The most commonly used therapeutic lasers in veterinary medicine are Class III lasers, which may deliver energy from 1mw to 500mw, and Class IV lasers, which deliver power at greater than 500mw.
- A lower watt laser provides less energy delivery to deeper tissues so the time needed to deliver a treatment is longer. A lower power laser is better suited for treating superficial structures because of the limited power density to drive photons into the deeper tissues.
- A higher watt laser allows the treatment to be delivered over a shorter period and involves administering the laser energy with a sweeping motion over the affected area. This sweeping motion may provide more complete coverage of the treatment area and may cover surrounding areas that could be causing secondary or referred pain. Pulsing of the laser beam may provide less heating of tissues at the surface while allowing for an adequate level of energy to reach the deeper target tissues, but more research is needed to define the optimal approach to a pulsed laser beam.
BENEFITS OF THERAPEUTIC LASER
Most responses of cells and tissues to therapeutic laser have been studied in in vitro models (cell culture). There appear to be many distinct benefits to using therapeutic laser for its tissue effects. Therapeutic laser has been demonstrated to relieve both chronic and acute pain by modulating peripheral nerve function and nerve conduction velocities. Laser energy increases the speed of tissue repair by increasing local microcirculation as well as stimulating the immune system and reducing inflammation. Laser energy also enhances collagen and muscle tissue development, which in turn enhances healing.
There are several important “downstream” tissue effects from the application of laser light. These effects include:
- Collagen synthesis which enhances wound healing
- Stimulation of nerve healing
- Enhanced healing of tendons, cartilage, and bones
- Reduced swelling from injury
- Modulation of degenerative tissue changes
- Mitigation of CNS damage following traumatic brain injury and spinal cord injury
When creating a treatment protocol for therapeutic laser, it is important to consider these effects in order to maximize patient outcome. The actual time the tissue is exposed to light energy may also affect the outcome.
There are some important safety considerations when incorporating therapeutic laser into treatment protocols. Protective glasses with lenses rated to the specific wavelength of the treatment laser are important for both humans and patients in order to protect retinal tissue. Laser energy should not be applied over a pregnant uterus, over tumors, over an open fontanel, over the growth plates of immature animals, or over the thyroid gland. Be careful if the pet has a tattoo, black fur, or black skin because of the potential for light absorption and tissue heating.