By Pat Anson, Editor

Many people who suffer from migraines will tell you that bright light can trigger a horrible headache.

But researchers at Beth Israel Deaconess Medical Center in Boston have found that a narrow band of green light can significantly reduce light sensitivity – known as photophobia – and reduce headache severity in migraine sufferers.

"Although photophobia is not usually as incapacitating as headache pain itself, the inability to endure light can be disabling," said Rami Burstein, PhD, Vice Chair of Research in the Department of Anesthesia, Critical Care and Pain Medicine and Academic Director of the Comprehensive Headache Center at Beth Israel Deaconess, as well as the John Hedley-Whyte Professor of Anaesthesia at Harvard Medical School.

"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."

Five years ago, Burstein and his colleagues made the surprising discovery that blue light hurts migraine patients who are blind. The finding prompted research that found photophobia could be alleviated by blocking blue light. However, because that study involved only blind patients, who cannot detect all colors of light, researchers devised a way to study the effects of different colors of light on headache in patients who are not visually impaired.

In the first study of its kind, published in the journal Brain, Burstein and colleagues found that a narrow band of green light worsens migraine significantly less than other colors of light, and that low intensities of green light can even reduce headache pain.

The researchers asked 43 patients experiencing acute migraine attacks to report any change in headache when exposed to different intensities of blue, green, amber and red light.

As the intensity of the light increased every 30 seconds, patients were asked if their headache intensified. Nearly 80 percent of patients said their migraines got worse when exposed to white, blue or amber light, while green light was found to reduce pain in 20 percent of patients.

Researchers then measured the magnitude of the electrical signals generated by the retina (in the eye) and the cortex (in the brain) of patients in response to each color of light. They found that blue and red lights generated the largest signals in both the retina and the cortex, and that green light generated the smallest signals.

Researchers also used laboratory rats to study neurons in the thalamus, an area of the brain that transmits information about light from the eye to the cortex. These neurons were found to be most responsive to blue light and least responsive to green light, explaining why the migraine brain responds favorably to green light.

"These findings offer real hope to patients with migraines and a promising path forward for researchers and clinicians," said Burstein.

Burstein is now working to develop a more affordable light bulb that emits "pure" (narrow band wavelength) green light at low intensity, as well as affordable sunglasses that block all but this narrow band of pure green light. Currently, the cost of one such light bulb is prohibitively high ($360 to $500, according to this research) and the technology to block all but pure green light in sunglasses is also very costly.

Light therapy – also known as infrared or laser therapy – is also being used to treat pain from aching joints, muscles and low back pain. Red and green light are also used as a treatment for skin disorders such as acne, aging spots and wrinkles. The theory is that light therapy increases circulation and stimulates the growth of collagen in skin.

About a billion people worldwide suffer from headaches caused by migraines, which affect three times as many women as men.

Migraine affects about 36 million adults in the United States, according to the American Migraine Foundation. In addition to headache pain and nausea, migraine can cause vomiting, blurriness or visual disturbances, and sensitivity to light and sound. About half of people living with migraine are undiagnosed.