People who are hung over or suffer from migraines know that wearing tinted lenses not only makes you look cool, it helps ease the pain.
Therefore it’s not surprising that custom tinted lenses have been widely used to decrease visual perceptual distortions in poor readers, and are being used more for migraine sufferers, but to date the science behind these effects has been uncertain. Currently research published in the journal Cephalalgia, by SAGE, uses functional magnetic resonance imaging (fMRI) for the first time to propose a neurological foundation for these visual therapies.
The new research displays the way colored glasses adjusted to each migraine sufferer work by regulating activity in the brain. The researchers spotted specific abnormal brain activity (known as hyperactivation) when migraine sufferers saw strong patterns. The shaded lenses considerably reduced the effect.
Jie Huang and colleagues from Michigan State University and the University of Michigan, and the University of Essex, UK, targeted specific visual stimuli known to trigger migraines. These patterns, high contrast stripes or 'gratings,' can give the appearance of shape, color and movement. These not only initiate migraines but also may cause seizures in those with photosensitive epilepsy.
Before the brain imaging took place, participants were tested and prescribed precision ophthalmic tints (POTs) with an Intuitive Colorimeter. Previous studies have recommended that some 42% of migraine with aura sufferers saw their migraine occurrences cut in half on days when they wore POTs.
The scientists used the colorimeter to light up text with colored light, manipulating hue and saturation at constant luminance. For each test participant this gave an optimal hue and saturation (chromaticity) of light that led to the greatest comfort, reducing perceptual distortion. The test subjects then viewed stressful striped patterns illuminated with their optimal colored light settings to screen for efficacy. The researchers used these readings to generate both effective POTs for each migraine sufferer and also two other pairs of grey and colored lenses with slightly different properties as controls. 11 patients who regularly suffered from migraines enrolled in the fMRI study. Each patient was matching with a migraine-free control, who was also tested with that patient's three sets of lenses.
Once in the fMRI machine, the researchers exposed subjects to a series of striped patterns – these had varying likelihood of triggering distortion and discomfort. This study’s goal was to investigate the effect of the POTs on the cortical activation induced by the stressful pattern in each of the visual areas of the brain. While patients reported some relief using all of the lenses (by around 40%), the POT lenses had a significant effect when viewing the stressful stripes (70% discomfort reduction). Both control and migraine patients responded similarly to the non-stressful stripe patterns, and in these cases all three lenses made no difference to the result. The POTs specifically suppressed cortical activation for migraine sufferers in visual area V2 of the occipital cortex of the brain, and this POT-suppressed cortical activation was also extended to the other extra-striate visual areas V3, V3A, and V4.
"The reduced cortical activation in V2 by the POTs may have been responsible for the POT-induced suppression of the illusions and distortions, considering that V2 neurons but not V1 neurons in macaque monkeys respond to illusory contour stimuli," Huang suggests.
The source of these responses to specific visual stimuli is expected to differ from the photophobia (light sensitivity) migraine sufferers often report during an attack. Going forward, the authors propose that the specific characteristic of the cortical activation in the extra-striate visual areas they recorded could deliver a potential biomarker for identifying those migraine patients suffering cortical hyperactivation. This biomarker could be useful not only for further evaluation of POTs but also for reviewing the efficiency of drugs to prevent migraines.