Lasers: Applications for therapeutic use

Answers to frequently asked questions you need to know


(NICK KOUDIS/GETTY IMAGES)
You've seen them at conferences and heard about them in lectures. In case you missed the discussion, therapeutic lasers are taking hold in veterinary medicine. Why? Because they work.

But you should know some of the facts and the basic science behind this technology so you can ask the right questions before you purchase one.

Laser stands for light amplification by stimulated emission of radiation. Cold or low-level laser therapy (LLLT) is relatively new in the United States, having gained FDA approval in 2002. It has, however, been used for many years in other parts of the world, including Canada, Australia, Europe and some Asian countries. Randomized controlled trials, systematic literature reviews and meta-analyses now being conducted are supporting the effectiveness of lasers in treating pain and making recommendations regarding dosages and machine specifications.

How does laser treatment reduce patients' pain?

Lasers can reduce pain in several ways. One review paper cited the anti-inflammatory effects of laser treatment as similar to those of pharmacologic agents such as celecoxib, meloxicam, diclofenac and dexamethasone.1 Lasers also can control pain by reducing oxidative stress, improving angiogenesis and augmenting collagen synthesis and skeletal repair.2 A randomized controlled trial showed that lasers were able to inhibit transmission at the neuromuscular junction, which reduced nerve firing and pain signaling.3 In a meta-analysis of laser use in people, laser therapy was shown to decrease neck pain immediately, with positive effects that could last up to three months after the end of a treatment series.4

What other benefits can laser treatment offer patients?

Lasers also have been shown to improve tendinopathy lesions. Research validates that injured soft tissues exposed to laser light demonstrate an increase in collagen synthesis, improved metabolism of tenocytes or myocytes, increased fibroblastic activity, neovascularization, improved tensile strength, acceleration of the healing process and organization of collagen bundles. LLLT also is widely used and found to be effective in treating chronic joint disorders, enhancing biosynthesis of cartilage, stimulating microcirculation and reducing inflammation in the synovium and synovial fluid.

Bone healing is another indication for LLLT. Improvement is seen as osteoblastic proliferation, bone neoformation, bone stiffness, collagen deposition, amount of well-organized trabeculae and creation of a smaller, stronger callus. Exposure to laser light can also promote wound healing, reducing wound size and healing time. Laser therapy has also shown impressive results in remediation of peripheral nerve injuries and even spinal cord lesions.

Can laser therapy be dangerous?

The editors of a recent special edition of Physiotherapy Canada thoroughly reviewed contraindications and precautions for laser therapy.5 They determined it should not be used over the eyes or reproductive organs or in regions known or suspected of malignancy. Laser therapy is not safe to use in regions with circulatory compromise or in patients with hemorrhagic disorders with actively bleeding tissues. Only experienced practitioners should use a laser on recently irradiated tissues or over the anterior neck or carotid sinus. Caution also should be taken in patients with photosensitivity disorders, infections and a compromised immune function or active epiphyses.

What do I need to know about phototherapy?

Laser light is collimated—it does not diverge. It possesses coherence and monochromaticity, which means when it's produced, it maintains a single wavelength. Human and animal studies have shown that body tissue tends to absorb and use wavelengths within the range of 600 to 1,000 nanometers (nm).

Laser machines come with one or multiple sets of predetermined wavelengths, and wavelength determines the penetration depth. Wavelengths within the 600-nm range do not directly penetrate more than 0.5 to 2 cm, or indirectly up to 5 cm, via the dissipation of energy. Wavelengths that range from the mid-700- to low-900-nm range penetrate the deepest, directly affecting tissues up to 5 cm and indirectly up to 10.

Light energy is measured in joules (1 joule = 1 watt Ă— 1 second). So a 500-milliwatt (mW) machine can deliver 1 joule of energy in two seconds, and a one-watt machine can deliver 1 joule of energy in one second. A 10-watt machine can deliver that same energy in 1/10th of a second. While being fast might be good if you want to deliver a large number of joules or treat a large area, it also means your laser technique must be modified to prevent superficial tissue damage.