Scientists illuminate migraine mystery

Scientists have solved the mystery of why migraine sufferers shun the light.

Light intensifies migraine headaches because of a particular group of retina cells at the back of the eye, research has shown.

These photoreceptors send signals to the brain along the optic nerve which then stimulate migraine pain neurons.

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Even small amounts of light are enough to affect the nerve pathway, sending victims running for the shadows.

People who are totally blind because of eye diseases such as retinal cancer and glaucoma are not affected by light during migraine attacks, the study found.

But this was not true of “legally blind” individuals with severely impaired eyesight, who cannot make out images but who can detect the presence of light.

Migraine is a one-sided, throbbing headache associated with symptoms that can include nausea, vomiting and fatigue.

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The pain is believed to develop when the meninges – the system of membranes that surround the brain – becomes irritated.

Nearly 85 per cent of migraine sufferers are highly sensitive to light, a condition known as photophobia, but until now no-one understood why.

Professor Rami Burstein, from the Beth Israel Deaconess Medical Centre in Boston, who conducted tests on totally and “legally” blind migraine sufferers, said: “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 grey wavelengths.

“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.”

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The scientists, whose findings are published online in the journal Nature Neuroscience, suspected that a group of recently discovered retinal cells which play a role in the body’s night and day cycle were involved.

They contain melanopsin photoreceptors, which help control biological functions such as sleep and wakefulness.

The light receptors are the only ones left working in patients who are “legally blind” and can sense light without being able to see shapes.

Laboratory animal tests confirmed the theory, revealing a direct link between melanopsin retinal cells and brain neurons that become electrically active during migraine attacks.

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