Wikimedia Commons/Sasha Wolff
In addition to pain, many migraine suffers experience light sensitivity that can greatly interfere with daily life. A team of researchers from Beth Israel Deaconess Medical Center in Boston, Mass., USA, says migraine photophobia may originate in the retinal neural pathway, and that a narrow band of green light could help soothe the suffering of people experiencing these painful and often debilitating headaches (Brain, doi: 10.1093/brain/aww119).
Five years ago, lead author Ravi Burstein found that blue light exacerbated migraine pain in patients who are blind. He said this discovery inspired him to investigate how different wavelengths of light could be linked to migraine symptoms and how light could perhaps be used to alleviate light sensitivity in patients without visual impairment.
Psychophysical and electrophysiological studies
Burstein and his colleagues asked 41 patients experiencing migraine attacks to report any change in pain levels when exposed to white, blue, green, amber and red light at different intensities. About 80 percent of the patients noted a worsening in pain for all colors of high-intensity light except green. In fact, the researchers report that green light appears to have reduced headache pain by about 20 percent.
To figure out why green light has this effect on people experiencing migraines, the researchers looked at the magnitude of electrical signals of ganglion cells in the retina and neurons in the cortex of the brain when patients were exposed to blue, green, amber and red light. Using electroretinography (basically, a reading of the retina’s electrical response when exposed to light), they observed that the largest signals in the retinal pathway and the visual cortex were generated from exposure to blue and red light, while green light generated the smallest signals.
Next, the team used rat models to study how neurons in the thalamus—the area of the brain that transmits signals from the retina to the cortex—respond to different colors of light. They found that blue light elicited the most responses in thalamic neurons and green elicited the least number of responses.
Results and future work
In addition to evidence that green light could sooth migraine-induced light sensitivity, the authors say that findings from their psychophysical assessment and animal studies suggest that photophobia could start in the retinal pathway, and then be “fine-tuned in relay thalamic neurons outside the main visual pathway, and preserved by the cortex.”
While not as debilitating as the pain associated with migraines, photophobia can greatly affect a person’s quality of life. Burstein says: “More than 80 percent of migraine attacks are associated with and exacerbated by light sensitivity, leading many migraine sufferers to seek the comfort of darkness and isolate themselves from work, family and everyday activities.”
Burstein and his colleagues hope to develop affordable light bulbs that emit low-intensity green light and sunglasses that block all but this narrow wavelength of light.