31/07/2018
SAD EYES
People with vision-loss could be three times more likely to develop Seasonal Affective Disorder (SAD)than those with normal vision, says a new study.
Nearly twice as many blind people suffer from Seasonally Effective Disorder (SAD) compared to people with normal vision. But those with poor vision suffer the most, concludes a new study.
If you are visually impaired, the risk of developing Seasonal Affective Disorder (SAD)--is almost three times as high as those with normal vision.
These are the conclusions of a new study published in the scientific journal British Journal of Psychiatry.
“It gives us a reason to investigate if the cause of a very complex disorder is actually to be found in the retina of the eye and not in the brain,” says Ba-Ali, who was not involved in the research.
Worse being visually impaired than completely blind
The study found that a higher proportion of people with vision loss suffered from SAD compared to people who were either totally blind or normal sighted.
In a survey of 1,647 blind and visually impaired people and 2,275 normally sighted people, 17.3 per cent of the visually impaired suffered from winter depression, whilst 13.2 per cent of the blind and 7.6 per cent of those with normal vision were affected.
The results came as a big surprise to the scientists behind the study.
"Reduced light has a significant impact on the development of winter depression, so our hypothesis was that blind people would develop winter depression more often than the general population,” says co-author Associate Professor Ida Hageman from, University of Copenhagen, Denmark, and head of the Psychiatric Centre Copenhagen.
“But we didn’t expect to see that people who still retain a perception of light would actually be the most [affected]," she says.
Partial sight is more dependent on light
So what is the explanation? Why is that partially sighted people are most affected by SAD?
Scientists do not really know. But many suggestions point towards SAD starting in the eyes.
"One possible explanation could be that there’s an upwards adjustment of specific photoreceptors--cells in the retina that monitor brightness--in the visually impaired,” says Ba-Ali.
“These photoreceptors are very important for synchronization of our internal biological clock to light and circadian rhythms," he says, adding that previous research from The Glostrup Eye Clinic, Denmark, suggests that some visually impaired people experience a bigger response in their photoreceptors, than those with normal vision.
This suggests that visually impaired people are more sensitive to changes in light, despite their poor vision.
Blind people may unknowingly perceive light
According to Hageman, it is possible that in some blind people, light still reaches the brain. This may help to explain why blind people seem to suffer less from winter depression compared to those with impaired vision.
