Laser therapy for pets is being seen more often. From relieving the signs of osteoarthritis to speeding up wound healing – there are many claimed benefits. 

Laser therapy, known as Low level laser (light) therapy (LLLT) and LED (light emitting diode) therapy, or photobiomodulation, has been suggested to have a beneficial reducing inflammation and oedema, inducing analgesia (pain relief), and promoting healing in a range of musculoskeletal disorders and injuries. But what is the evidence?

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What is laser therapy?

Laser Therapy or Photobiomodulation is a low intensity light therapy; the effect is claimed to be photochemical rather than thermal (heat). The light triggers biochemical changes within cells where the photons are absorbed by cellular photoreceptors and triggers chemical changes.

There are thought to be around four clinical targets for LLLT:

  • The site of injury – with the aim to promote healing, remodeling and reduce inflammation.
  • Lymph nodes, to reduce oedema and inflammation.
  • Nerves, to induce analgesia (pain relief).
  • Trigger points, to reduce tenderness and relax contracted muscle fibers.

What is the theory of its action?

For low-power visible or near-infrared light to have an effect on a biologic system, the photon must be absorbed by electronic absorption bands belonging to a photon acceptor or chromophore (a chromophore is a molecule, or portion of a molecule, which imparts a color to a compound).

Mitochondria, as everyone seems to remember from their biology lessons, are known as ‘the cellular power plants’ or ‘powerhouse of the cell’. Mitochondria convert food molecules and oxygen into energy (ATP) by oxidative phosphorylation. It has been proposed that cytochrome c oxidase (Complex IV) is the primary photo-acceptor for the red-NIR wavelength range in mammalian cells. Nitric oxide (NO) produced in mitochondria can inhibit respiration by binding to Complex IV and displace oxygen especially in injured or hypoxic cells, thus reducing their capacity. It is proposed that LLLT can photo-dissociate NO from Complex IV and reverse the mitochondrial inhibition of respiration due to excessive NO binding. 

This results in activation of cell-signaling mechanisms that promote proliferation and differentiation in an anti-inflammatory environment tightly regulated by the manipulation of oxidative and nitrative stress.

That’s a little complex, right? 

Basically, it is suggested that laser therapy, if absorbed by the cell in the correct area, promotes the efficacy of mitochondria at their role in cellular respiration. Thus are more effective at providing cells with energy. In theory making them more likely to work more effectively, heal or regenerate faster.

Are there different types of lasers?

In short, yes. There are different classifications of laser, and it is important to differentiate between them. Classification and effectiveness seem hard to correlate; classification is more to do with safety and hazard to the eye than its therapeutic potential. There appears to be not a substantial enough body of research to definitively say what class laser (primarily Class 3b or 4) or what power is most effective for results. The vast majority of studies revealing the effective mechanisms of laser therapy are done using a Class 3b laser. But very few studies compare a Class 3b to Class 4.

Laser classifications include: 

Class 1 and 2 are essentially the lasers found in classroom laser pointers; they’re generally considered safe although you still should not point them at someone’s face! It would take so long to deliver an effective amount of energy for healing, if it can even get the dose delivered into the tissue deep enough that; these lasers are essentially not going to be therapeutic. 

Class 3b are ‘cold’ lasers and are classified as being capable of causing damage to the eye. Safety glasses should be worn when using this class laser and above. The FDA defines this Class 3b as a power output at a maximum of 500mW as measured at a defined aperture and distance from the lens.

Class 4 lasers are almost identical to the Class 3b in therapeutic effect; but, with a higher power output, the risk of burning is higher with a Class 4 laser.

Penetration

For LLLT to be effective, the irradiation parameters (wavelength, power, power density, pulse parameters, energy density, total energy and time) need to be within certain ranges. The “optical window” in a tissue describes a range of wavelengths where the penetration of light into tissue is maximised by employing red and near-infrared wavelengths.

Penetration is variable, with one study finding that near infrared light in the range 770–850 nm penetrates deeper through rat tissue than red light or longer infrared wavelengths, up to 1200 nm. 

What is the evidence?

It is extremely challenging to compare LLLT to other treatments, as studies using LLLT are complicated by different lengths of treatment, different machines, and without standardisation of wavelengths and dosages.  

Pain

The peripheral nerve endings of nociceptors, consisting of the thinly myelinated and unmyelinated, slow-conducting C fibres, lie within the epidermis (the skin). In the pain pathway, this network of nerve fibres is used to transduce noxious (painful) stimuli into action potentials – to protect you from harm. These nerve endings are very superficial in nature and thus are within the penetration depths of the wavelengths used in LLLT. It is this theory that means there are several painful conditions that are suspected to be benefited by using laser therapy.

In one study on a rodent model, the use of laser stimulation increased the pain threshold (the level of stimulation at which pain is perceived) by a factor between 68% and 95%, depending on the injected drug.

In another study, repeated irradiation with a low-power laser produced relief in subjects with chronic pain. Analgesia was observed after exposure of the skin overlying the radial, medial and saphenous nerves; and in some cases, irradiation of the appropriate painful nerve. What this suggests to me is that when attempting to treat animals for chronic pain, we shouldn’t necessarily just be focusing on the painful area (e.g. it has hip pain so let’s use the laser on the hip). But more specifically, and indeed with great knowledge of anatomy, be focusing on the specific peripheral nerves associated with the pain. Whether this happens in a clinical setting is another matter and could explain the variable results seen when applied. 

Wound Healing

LLLT at low doses has been shown to enhance cell proliferation (multiplication) of: 

  • Fibroblasts – cells that synthesise the extracellular matrix and collagen, produce the structural framework (stroma) for animal tissues, and play a critical role in wound healing
  • Keratinocytes – the primary type of cell found in the epidermis, the outermost layer of the skin)
  • Endothelial cells lining blood vessels
  • Lymphocytes – immune cells that are made in the bone marrow and are found in the blood and in lymph tissue). 

All fairly useful cells when it comes to wound healing!

The mechanism of proliferation is thought to result from photo-stimulation of the mitochondria. This leads to activation of signalling pathways and up regulation of transcription factors. Eventually, this gives rise to increasing levels of growth factors, triggering increased cell multiplication.

LLLT can also enhance neovascularisation (the formation of new blood vessels); promote angiogenesis (the development of blood vessels); and increase collagen synthesis to aid in the healing of acute and chronic wounds.

Conclusion

It is difficult in a short article to cover all points needed (and all the specific conditions that laser has been studied in). But overall, there are a few things to conclude. 

There is some evidence to suggest that laser therapy, when used at the wavelength could be useful clinically to some conditions. At present, there is a mismatch of studies but the variation on machines used, and settings does make it difficult for us to fully draw strong conclusions. 

When looking at if laser therapy will be effective, we currently don’t fully know the mode of action. But we have a lot of very plausible theories and in vitro studies (done in laboratory setting); which when applied to a clinical setting do appear to see some positive results. If finances are sensitive, there may be more evidence-based modalities to direct those finances to. Overall, laser MAY be a useful adjunct to some treatment plans for some ailments. But it should not be relied on solely as the management.

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