For the 36 million Americans who suffer from migraines, sensitivity to light is but one of the many disorienting, sometimes sickening symptoms they have to manage. The condition is formally known as photophobia, something a team of researchers from Harvard Medical School aimed to better understand by giving volunteer sufferers a variety of color tests. Their findings, published in the journal Brain, reveal low-intensity green light can significantly reduce migraine pain.

Researchers exposed 69 migraine patients to different wavelengths of light, including blue, red, green and amber through a pair of color-tinted glasses. They asked patients who were experiencing migraines to report any changes when shown different colors. As they were doing this, researchers measured the electrical signals generated by the retina, the light-sensitive layer of eye tissue, to the brain in order to see if there were changes in activity based on each color.

Results showed that the green light generated the smallest amount of electrical signals in both the retina and the brain, indicating that there was less stimulation. Patients said the low-intensity green light was able to ease the pain of migraines by 20 percent, while the other colors increased patients' pain.

“We were surprised to see that blue light was no more painful than white or amber or red. They were all painful,” said the study’s lead author Rami Burstein, a professor of anesthesia at Harvard Medical School, in a statement. "It is their inability to endure light that most often disables them."

Experts have yet to trace the root cause of a migraine, which is why finding an effective treatment continues to be difficult. However, there are certain migraine triggers that have been identified, which can raise the risk of having a migraine attack, such as hormonal changes, weather, lights, smalls, alcohol, foods, poor sleep, and higher levels of stress.

Photophobia, which is linked to more than 80 percent of migraine attacks, is not as incapacitating as the pain of the migraine headaches itself, but it is one of the most difficult symptoms to live with, ultimately isolating sufferers.

"Although photophobia is not usually as incapacitating as headache pain itself, the inability to endure light can be disabling," Burstein said. "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."

Researchers aren’t sure why the green light is able to alleviate some of the migraine pain the patients were experiencing. They suspect, though, that it may have something to do with the way green wavelengths travel through the eyes and into the cortex of the brain near the thalamus, the region where photophobia stems from.

Burstein and his team are now trying to develop an affordable light bulb that can emit the same low-intensity green light that they used in the experiment. They’re also experimenting with a design for sunglasses to block all wavelengths of color expect for the particular green band of light.

"My hope is that patients will be able to benefit directly from these findings one day very soon.” Burstein said. “In general, it seems a safe treatment but one that is limited by cost, access, and whether its use on a regular basis would decrease disability.”

Source: Burstein R, Noseda R, and Bernstein CA. Migraine photophobia originating in cone-driven retinal pathways. Brain. 2016.