Ask anyone who suffers from migraine headaches what they do when they’re having an attack, and you’re likely to hear “go into a dark room.”
And although it’s long been known that light makes migraines worse, the reason why has been unclear.
In a new study, researchers have identified a new visual pathway that underlies sensitivity to light during migraines in both blind individuals and in individuals with normal eyesight.
The findings can help explain the mechanism behind this widespread condition.
The research was conducted by scientists at Beth Israel Deaconess Medical Center (BIDMC)
A one-sided, throbbing headache associated with a number of symptoms, including nausea, vomiting, and fatigue, migraines are notoriously debilitating and surprisingly widespread, affecting more than 30 million individuals in the U.S. alone.
Migraine pain is believed to develop when the meninges, the system of membranes surrounding the brain and central nervous system, becomes irritated, which stimulates pain receptors and triggers a series of events that lead to the prolonged activation of groups of sensory neurons.
In addition, for reasons that were unknown, nearly 85% of migraine patients are also extremely sensitive to light, a condition known as photophobia.
Even the dimmest of light can make migraine pain worse. Extremely disabling, photophobia prevents patients from such routine activities as reading, writing, working, or driving.
It was the observation that even blind individuals who suffer from migraines were experiencing photophobia that led the team to hypothesize that signals transmitted from the retina via the optic nerve were somehow triggering the intensification of pain.
The 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; they were unable to see images or to sense light and therefore could not maintain normal sleep-wake cycles.
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.
The team found 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, in particular blue or gray wavelengths.
This suggested 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.
The scientists then performed a series of experiments in an animal model of migraine.
After injecting dyes into the eye, they traced the path of the melanopsin retinal cells through the optic nerve to the brain, where they found a group of neurons that become electrically active during a migraine.
They discovered that light was triggering a flow of electrical signals that were converging on these very cells. This increased their activity within seconds.
And even when the light was removed, these neurons remained activated.
This helps explain why patients say that their headache intensifies within seconds after exposure to light, and improves 20 to 30 minutes after being in the dark.
The discovery of this pathway provides scientists with a new avenue to follow in working to address the problem of photophobia.
The team says clinically, this research sets the stage for identifying ways to block the pathway so that migraine patients can endure light without pain.
One author of the study is Rami Burstein, Ph.D., Professor of Anesthesia, and Critical Care Medicine at BIDMC and Harvard Medical School.
The study is published in Nature Neuroscience.
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