For most migraine and post-traumatic headache sufferers, light reveals nothing but problems. Increased sensitivity to light — or photophobia — means participation in everyday activities can become difficult and often the only solution is a dark room. Brightening their prospects, then, a new study from Harvard shows how exposing sufferers to pure-wavelength green light can significantly reduce photophobia and can even the severity of their headaches.
Photophobia is associated with more than 80% of migraine attacks and although it is not as incapacitating as the pain of the headache itself, for migraine sufferers, "it is their inability to endure light that most often disables them," says Harvard Medical School's Rami Burstein, lead author of the study. Both natural daylight and indoor electric light are made up of a wide range of colors that are made up of different light wavelengths. The researchers — publishing in the journal Brain — explain how a narrow band of green on the spectrum can cause significantly less aggravation to sufferers than all other colors of light and that at low intensities it can even reduce a headache.
Burstein's team devised a way to study the effects of different colors of light on headaches in patients with normal vision after discovering that blind migraine patients are only negatively affected by blue light. They asked patients experiencing acute migraine attacks to describe any changes they felt when exposed to different intensities of blue, green, amber and red light. At high intensity of light — like that in a well-lit office — nearly 80% of patients reported intensification of their headache. When they selected different colors of light, this reaction was true for all wavelengths except green. Unexpectedly, the team found that green light actually reduced their pain by around 20%.
This anomaly was explained when the researchers looked at the level of electrical signal generated in the retina (the light-sensitive layer inside the eye) and in the brain's visual cortex as light hit the eye. By measuring electrical response to each color, they found that green light generated the smallest signals in both the retina and cortex. This, they say, is because of the way the thalamus — the part of the brain that sends information about light from the eye to the cortex — changes that information meaning blue and red light are more painful than green.
"My hope," says Burstein, "is that patients will be able to benefit directly from these findings one day very soon." His hope is eventually to create a low-cost light bulb that can emit "pure" green light (that is, light of a specific narrow-band wavelength) at low intensity and combine them with sunglasses that block all but this narrow band of pure green light. Though the technology is currently prohibitively expensive, he says, it could one day bring relief to migraine sufferers worldwide.