Review of light parameters and photobiomodulation efficacy: dive into complexity

Abstract

Photobiomodulation (PBM) therapy, previously known as low-level laser therapy, was discovered more than 50 years ago, yet there is still no agreement on the parameters and protocols for its clinical application. Some groups have recommended the use of a power density less than 100 mW∕cm 2 and an energy density of 4 to 10 J∕cm 2 at the level of the target tissue. Others recommend as much as 50 J∕cm 2 at the tissue surface. The wide range of parameters that can be applied (wavelength, energy, fluence, power, irradiance, pulse mode, treatment duration, and repetition) in some cases has led to contradictory results. In our review, we attempt to evaluate the range of effective and ineffective parameters in PBM. Studies in vitro with cultured cells or in vivo with different tissues were divided into those with higher numbers of mitochondria (muscle, brain, heart, nerve) or lower numbers of mitochondria (skin, tendon, cartilage). Graphs were plotted of energy density against power density. Although the results showed a high degree of variability, cells/tissues with high numbers of mitochondria tended to respond to lower doses of light than those with lower number of mitochondria. Ineffective studies in cells with high mitochondrial activity appeared to be more often due to over-dosing than to under-dosing.

Effects of Low-level Light Therapy at 740 nm on Dry Eye Disease In Vivo

“…Although LLLT with inadequate parameters may be ineffective and even cause unwanted inhibitory effects, 22 what is known regarding LLLT and its parameters is still at basic level, and more information should be needed to define accurate parameters. 39,40 In summary, this study confirmed the effect of LLLT at 740 nm in vivo on DED mouse model. The LLLT at 740 nm was considered effective in treating DED, increasing tear volume, improving corneal surface irregularities and symptom scores, alleviating inflammation through decreasing the levels of neutrophils and inflammatory cytokines such as IL-1β, IL-6α, and TNF-α.…”

1064 nm Nd:YAG laser light affects transmembrane mitochondria respiratory chain complexes

“…The effect is not dose‐dependent nor, represented by the Arndt–Schultz law of biphasic dose response, which represents a foundational concept of PBM, as suggested by Zein et al . The 1064 nm‐mitochondria interaction, under the used conditions, shows reasonably window effects with a narrowed range of tolerability.…”

Photobiomodulation Therapy Associated with Heterologous Fibrin Biopolymer and Bovine Bone Matrix Helps to Reconstruct Long Bones

“…In addition to specific treatments, rehabilitation therapy by techniques complementary to therapeutic treatment has been increasingly applied, especially photobiomodulation therapy (PBMT), with the use of low intensity laser [8,13,[16][17][18]. Its photon energy reaches the cell nucleus increasing the synthesis of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) and consequent protein synthesis [19]. Furthermore, it increases the adenosine triphosphate (ATP) and cellular mitotic activity [20].…”

“…This new technology is the current focus of studies of the scientific community for presenting reparative mechanisms of action. However, there is no consensus on its effective parameters, because if parameters are not properly delineated, they do not have beneficial effects on tissue regeneration, making this a current focus of research [19,21,[23][24][25].…”