The effects of blue on dyslexia
Coloured filters, either worn as spectacles or used as overlays, have been successfully employed in the treatment of dyslexia for many years but there is no agreement about how they work.
Bright white light increases the activation of the parts of the brain involved in directing attention, such as the posterior parietal cortex.
Abnormal function in these attention-modulating parts of the brain has been implicated in the pathogenesis of dyslexia.
It is therefore likely that blue light selected optimally to recruit ipRGCs will have the greatest effect on improving alertness and concentration and may therefore be the best for remediating the impaired attentional responses seen in dyslexia.
The DRT has carried out a randomised control trial that showed that in suitable dyslexic children wearing blue filters for 3 months improved their reading age by an amazing 9 months.
The effects of blue light on sleep
Blue light therapy has been shown to help people with sleeping problems, to improve alertness during night shift work and to help overcome jet lag.
It probably works on the suprachiasmatic nucleus to alter the timing of diurnal rhythms. We found that children whose reading benefitted from wearing blue filters during the day often reported also that their sleeping patterns had improved, and we showed that this was probably due to an effect on the SCN; at night secretion of the sleep hormone, melatonin, which is also under the control of the SCN, can be inhibited by just 15 minutes of blue light ie blue light can reset the SCN rhythms to improve sleeping.
The effects of blue light on migraine
Likewise we found that in these dyslexics, who often complain of migraine type headaches, the blue filters often improved their headaches.
Migraine was previously thought to be due to swelling of the arteries in the membranes surrounding the brain, the meninges, but we now believe that the hypothalamus and specifically the SCN is responsible.
Coloured filters, worn as spectacles, have been found to be highly effective in reducing the frequency of migraine symptoms. Their efficacy probably does not result from their effects on conscious visual perception via the retinogeniculocortical pathway, but rather by affecting the hypothalamus via the retinohypothalamic pathway.
So blue filters are the most efficacious in reducing migraine.
Light and Seasonal Affective Disorder
Seasonal affective disorder (SAD) is a depressive syndrome experienced by around 5% of the population, the symptoms of which recur in winter and autumn.
A number of experimental findings combined with the circannual pattern of symptom expression implicate disordered diurnal rhythms controlled by the SCN in the pathogenesis of SAD.
SAD symptoms are likely to be the result of an abnormal phase-delay in the circadian rhythm. Hence exposure to blue light, particularly in the morning, often improves SAD greatly.
Exposure to natural daylight at work and school is often minimal and fluorescent electric lighting is usual.
Unfortunately most fluorescent lights radiate very little short wavelength blue light.
Full spectrum fluorescent lights, the spectral output of which is similar to that of natural daylight, or blue light should therefore be superior for the promotion of human health and cognitive function because they stimulate the retinal hypothalamic system more effectively.
Dyslexia Research Trust - Vision & Coloured Filters