Highlights
- •Light provides analgesia through cutaneous application or visual stimulation.
- •Depending on wavelengths, visual stimuli may induce analgesia or hypersensitivity.
- •Light-induced analgesia relies on both central and peripheral mechanisms.
- •ipRGCs, RVM, and inflammation play a crucial role in phototherapy pain management.
- •Phototherapy for pain management is efficacious with scarce side effects.
Abstract
A growing body of evidence supports the modulation of pain by light exposure. As such,
phototherapy is being increasingly utilized for the management of a variety of pain
conditions. The modes of delivery, and hence applications of phototherapy, vary by
wavelength, intensity, and route of exposure. As such, differing mechanisms of action
exist depending upon those parameters. Cutaneous application of red light (660 nm)
has been shown to reduce pain in neuropathies and complex regional pain syndrome-I,
whereas visual application of the same wavelength of red light has been reported to
exacerbate migraine headache in patients and lead to the development of functional
pain in animal models. Interestingly visual exposure to green light can result in
reduction in pain in variety of pain conditions such as migraine and fibromyalgia.
Cutaneous application typically requires exposure on the order of minutes, whereas
visual application requires exposure on the order of hours. Both routes of exposure
elicit changes centrally in the brainstem and spinal cord, and peripherally in the
dorsal root ganglia and nociceptors. The mechanisms of photobiomodulation of pain
presented in this review provide a foundation in furtherance of exploration of the
utility of phototherapy as a tool in the management of pain.
Perspective
This review synopsizes the pathways and mechanisms through which light modulates pain
and the therapeutic utility of different colors and exposure modalities of light on
pain. Recent advances in photobiomodulation provide a foundation for understanding
this novel treatment for pain on which future translational and clinical studies can
build upon.
Key Words
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Article info
Publication history
Published online: February 23, 2021
Accepted:
February 9,
2021
Received in revised form:
January 26,
2021
Received:
October 29,
2020
Footnotes
Disclosures:
Dr. Ibrahim has a patent through the University of Arizona for using green light therapy for the management of pain. Dr. Slepian is a partner in a company to commercialize the green light therapy with Dr. Ibrahim. This work was supported by grants from the University of Arizona MD/PhD Program, NCCIH R01AT009716 (MMI), K08NS104272 (AMP), R01NS116694 (AMP), the Comprehensive Chronic Pain and Addiction Center-University of Arizona, and the University of Arizona CHiLLi Initiative.
Identification
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© 2021 by United States Association for the Study of Pain, Inc.
