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Laser treatment dosage in animal care

Why is the right dose crucial in photobiomodulation?

Photobiomodulation, or PBM, is used in veterinary medicine and animal rehabilitation. It involves red or near-infrared light interacting with biological tissues at the cellular level. The effect is not based on heating the tissue, but on the absorption of light by light-sensitive cellular structures, especially mitochondrial cytochrome c oxidase.

In light of current research, the effects of PBM are linked to cellular energy production, regulation of inflammatory responses, microcirculation, tissue repair processes and mechanisms related to nervous system pain modulation. In practical treatment situations, however, the decisive factor is not simply that a laser therapy device is being used, but what kind of biological dose ultimately reaches the target tissue.

This is why dosage is one of the most important questions in animal laser therapy. The same device, the same power or the same treatment time does not necessarily mean the same biological effect in different animals, different tissues or different treatment situations.

The dose response is not linear

Photobiomodulation follows a biphasic dose response. This is often referred to as the biphasic dose response phenomenon or the Arndt–Schulz curve. In practice, it means that the effect does not increase in a straight line as the dose increases.

Too small a dose may be biologically insufficient. An appropriate dose may produce the desired biological response. Too large a dose, on the other hand, may reduce the response, even when no actual tissue damage occurs.

This is a key principle in PBM. In laser therapy, the goal is not automatically the highest possible power or the highest possible total energy. It is more important to assess what kind of dose reaches the target tissue and what type of response is being sought.

In veterinary medicine, the dose is often expressed as energy density, in joules per square centimetre. In practice, however, the dose delivered to the surface and the biological dose that reaches the target tissue are not the same thing. Light attenuates in tissue, and this attenuation is affected by factors such as coat, pigmentation, tissue thickness, adipose tissue, muscle mass and the wavelength used.

Which factors affect dosage?

Dosage is influenced both by the technical properties of the device and by the tissue properties of the animal. Wavelength partly determines how light behaves in tissue. Red light in the range of approximately 600–700 nanometres is absorbed more effectively by superficial tissues and, according to research, is especially suited to applications involving skin, wounds, mucous membranes and superficial muscles.

Near-infrared light in the range of approximately 800–1100 nanometres generally travels through tissue more effectively than red light. This is why it is often used when the target area involves deeper muscle regions, joint areas, tendon structures or larger animals. This does not, however, mean unlimited penetration. Light intensity decreases in tissue, which is why treatment technique, contact, treatment time and the optical properties of the tissue are highly important.

Power and irradiance, meaning power density, are central to dosage. Higher power can allow a shorter treatment time, which can be practically useful for large treatment areas. However, the biological response does not depend only on total energy. The same total energy can produce a different response if it is delivered at a different power density or over a different period of time.

PBM protocols often use relatively low or moderate irradiance levels, because the aim is to optimise the biological response and minimise thermal effects. Excessively high irradiance can shift the effect in a more thermal direction or weaken the cellular response. This is especially relevant in animals, because coat and pigmentation can affect both light absorption and heat dissipation.

The optical properties of tissue change the actual dose

In animal laser therapy, tissue optics are highly important in practice. The way light travels is affected by coat, pigmentation, skin thickness, adipose tissue, muscle mass and tissue water content. This is why the same surface dose does not necessarily lead to the same biological dose in the target tissue.

A dark, long or dense coat can absorb and scatter light before it reaches the skin and deeper tissues. Shortening or clipping the coat can, in some situations, improve light delivery into the tissue. Pigmentation also matters: melanin absorbs especially visible red wavelengths, which means that dark skin or a dark coat can significantly reduce the amount of light reaching the tissue.

Tissue depth is another central factor. Deep structures, such as equine tendons, large muscle groups or areas such as the hip joint, often require a higher surface dose than superficial tissues. In horses and large dogs, the target structures may be located deeper than in small dogs and cats, which affects practical dosage planning.

The nature of the condition being treated also affects dosage. In acute situations, lower doses and more frequent treatment intervals are often used, whereas in chronic situations the doses may be higher and the intervals less frequent. This is not a mechanical rule, however. Clinical assessment is always based on the animal, the tissue, the treatment area and the observed response.

Typical dose ranges in veterinary studies

There is no universal PBM dose that suits all animals, tissues and situations. However, the dose ranges used in the literature tend to fall fairly consistently within certain surface dose ranges.

The table below describes dose ranges typically used in different sources. It is not an individual treatment guideline, but a general summary of the types of surface doses that have been used for different tissue types and treatment situations.

Tissue type / indication Typical dose range (J/cm²) Typical practice Notes
Superficial tissues, such as wounds, skin, mucous membranes and superficial muscles 2–6 Often 3–4 J/cm² 660 nm is effective; non-contact or light contact
Deep tissues, such as joints, tendons and deep muscles 8–20 Dogs: 8–15 J/cm². Horses: 10–20 J/cm² Near-infrared, 800–1100 nm; contact technique recommended
Osteoarthritis / chronic pain 8–15 Start at 8–12 J/cm² and increase as needed Often 2–3 times per week
Tendon injuries / acute trauma 10–20 Frequent treatment during the first week Coat has a strong effect
Post-operative situations 4–10 Lower dose during the first 3–5 days Often daily at the beginning

 

The truly optimal dose always depends on several variables: tissue depth, wavelength, irradiance, contact technique, size of the treatment area, the animal’s coat and pigmentation, and how the animal responds to treatment as part of the broader care plan.

Treatment frequency and response assessment

In acute situations, PBM is often applied at frequent intervals, especially during the first week. In practice, this may mean several treatments during the first week and, when needed, daily treatment. The aim is to support the tissue’s biological response at an early stage.

In chronic situations, treatment frequency is often lower. For example, two or three treatments per week are commonly used, after which treatment may continue at a less frequent maintenance rhythm. Treatment series often consist of several sessions, and the response is assessed as part of the overall picture.

Response monitoring is one of the most important practical measures. The effect of treatment can be assessed through factors such as pain, mobility, swelling and functional response. If the response remains weak, the first conclusion is not necessarily that laser therapy “does not work”. Often it is necessary to reassess the dose, technique, contact, treatment frequency, choice of treatment area and the animal’s overall situation.

Treatment technique affects the biological dose

In laser therapy dosage, treatment technique is just as important as the technical values of the device. Contact technique often improves light delivery into the tissue compared with non-contact use. When the treatment head is in contact with the skin, reflection is reduced and a larger proportion of the light can travel into the tissue.

A moving scanning or grid technique can help distribute energy more evenly over a wider area. This is practical especially when treating larger muscle areas or several adjacent treatment points. The aim is to avoid uneven dosing and ensure that the treatment area is treated consistently.

Preset programs can provide a good starting point for practical work, but the user still needs to understand the basic principles of tissue optics and dosage. Coat, pigmentation, tissue depth and the size of the treatment area may require adjustments to technique or dose. This is particularly important in veterinary medicine, where differences between species and individuals can be substantial.

Safety as part of dosage

When used correctly, photobiomodulation is generally well tolerated. Safe use requires that the user knows the device, follows the instructions for use and takes both the animal and the environment into account.

Direct eye exposure must always be avoided, and appropriate protective eyewear is part of laser therapy device use. With higher-powered devices, possible thermal effects must be considered, especially with dark coats or pigmented skin. Active tumours and other special situations should be assessed case by case.

Although serious adverse effects are rare in PBM, a biological inhibitory response is possible if the dose is too high. This means that safety is not only about avoiding tissue damage, but also about choosing a biologically appropriate dose.

Why dosage cannot be copied directly from human medicine

The WALT recommendations provide a useful basis for understanding photobiomodulation dosage in humans. In veterinary medicine, however, they should not be applied by direct copying.

In animals, coat, pigmentation, tissue depth, size differences and species-specific anatomical differences can significantly alter the actual dose reaching the target tissue. For this reason, the surface dose used in animals often needs to be assessed differently than in humans so that a sufficient amount of biologically active light reaches the target tissue.

This is one reason why understanding the whole treatment context is so important in animal laser therapy. Successful treatment does not depend only on what the device emits, but on how much biologically active light reaches the right tissue, at the right wavelength, with suitable irradiance and an appropriate dose.

Summary

Laser therapy dosage in veterinary medicine is based on the combined effect of biology, tissue optics and treatment technique. The effect of photobiomodulation is not linear: too small a dose may be ineffective, while too large a dose may reduce the biological response.

Practical dosage is affected by wavelength, irradiance, treatment time, the optical properties of the tissue, coat, pigmentation, tissue depth, animal size and treatment technique. Preset programs can provide a good starting point, but clinical assessment and an understanding of the biological dose remain essential.

In animal laser therapy, success is not based only on the device or a single device specification. The decisive factor is whether the right type of light reaches the right tissue at a biologically appropriate dose and in a repeatable way.

Sources

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