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Friday, December 13, 2019

Will You Go Blind In The Dark?

     I was watching a program on the History Channel the other day and there was a comment that spending three days in total darkness will lead to permanent blindness. Is that true? 
     A question that has long intrigued scientists and been the subject of hot debate is why do animals that live in caves become blind? There are thousands of underground and cave-dwelling species, from naked mole rats to bats, and many have lost their sense of sight. 
     Darwin originally suggested that eyes could be lost by "disuse" over time, but Reed Cartwright, an evolutionary biologist in the School of Life Sciences and researcher at the Bio-design Institute has suggested that eyes are not lost by disuse, but rather by natural selection - blindness was selected as favorable and the best for living in a cave. 
     It is claimed that if an individual is left in dark for three or more days, then the individual is at risk of losing his eyesight permanently.  However, I also read that there is no practical research supporting this fact and it’s only a myth like sitting too close to the TV for long enough makes you blind. More info...
     There was an article on the American Optometric Association’s website that stated soccer team members rescued from a Thailand cave could face temporary vision struggles. 
     In June and July of last year a widely publicized cave rescue was carried out where members of a junior soccer team were successfully extricated from Tham Luang Nang Non cave in Chiang Rai Province, Thailand after heavy rains partially flooded the cave, trapping the 12 boys and their coach inside.
     According to the article, in the dark, not only is your central vision greatly affected, but also peripheral vision. As a result it was expected that they would experience a relatively short period of light sensitivity after their rescue. 
     One optomotrist who comes from a long line of coal miners and practices optometry in West Virginia expected them to be extremely uncomfortable when they arrived at the surface, seeing light for the first time in weeks, as the pupil attempts to constrict and limit the amount of light entering the eye. He explained that light can be blinding in the same way as when a patient has their eyes dilated and they find light to be extremely bright, leaving them with spots in their vision. This blindness does not last as retinal pigment is regenerated.
     Doctors of optometry didn'texpect any long-term effects for the boys. In the dark, not only is your central vision greatly affected, but also peripheral vision which is an integral part of our body's balance system. If you stand on one leg with both eyes open, then shut both eyes, almost immediately you begin to wobble while the only thing that has changed is your visual input. 
     So, these young men also may have had issues with not only seeing in the cave, but also trying to remain balanced and feeling balanced, especially with the uneven terrain of the cave. This, added to an already compromised situation both mentally and physically, would have added significantly to their stress levels.
     Some insight into their eyes' reaction to being deprived of light for an extended time was gleaned from the 2010 rescue of 33 Chilean miners who were trapped underground for two months. They emerged reportedly wearing special sunglasses and their hospital rooms were kept in low light for a few days. Only one miner had reported experiencing long-term effects. 
     Paul Barney, a Doctor of Optometry that practices in Alaska, a state known for its extended periods of sunshine and darkness, stated, "Total light deprivation might cause a temporary loss of vision after a few days of being in the dark, but their vision would return to normal after a few hours of being in light." 
     Researchers at the Laboratory for Magnetic Brain Stimulation, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts report the occurrence of visual hallucinations of varying complexity in 13 normal subjects after sudden, complete, and prolonged visual deprivation. 
     The subjects wore a specially designed blindfold for a period of five consecutive days (96 hours) and were asked to record their daily experiences using a hand-held micro-cassette recorder. Ten of the subjects reported visual hallucinations, which were both simple (bright spots of light) and complex (faces, landscapes, ornate objects). The onset of hallucinations was generally after the first day of blindfolding. Subjects were insightful as to their unreal nature. 
     These results indicate that rapid and complete visual deprivation is sufficient to induce visual hallucinations in normal subjects. However, the study noted that vision returned to normal approximately 30 to 60 minutes after sight restoration. This would seem to relegate the theory that you will go blind after three days in totally darkness to a busted myth. 

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