Many people who suffer from migraine headaches head to a dark room when they're having an attack, but scientists weren't sure why it helped.

More puzzling, perhaps, was that blind people also seemed to feel better in the dark.

Researchers at Beth Israel Deaconess Medical Center said they have found a new visual pathway that senses light.

Rami Burstein said that nearly 85 percent of migraine patients are extremely sensitive to light. His team studied two groups of blind individuals who suffer migraine headaches.

Patients in the first group were totally blind due to eye diseases such as retinal cancer and glaucoma. Patients in the second group were legally blind due to retinal degenerative diseases such as retinitis pigmentosa; although they were unable to perceive images, they could detect the presence of light and maintain normal sleep-wake cycles.

"While the patients in the first group did not experience any worsening of their headaches from light exposure, the patients in the second group clearly described intensified pain when they were exposed to light," Burstein said. "This suggested to us that the mechanism of photophobia must involve the optic nerve, because in totally blind individuals, the optic nerve does not carry light signals to the brain.

"We also suspected that a group of recently discovered retinal cells containing melanopsin photoreceptors [which help control biological functions including sleep and wakefulness] is critically involved in this process, because these are the only functioning light receptors left among patients who are legally blind," a news release said.

The discovery of this pathway provides scientists with a new avenue to follow in working to address the problem of photophobia, the researchers said.