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I often find it physically painful to open my eyes past a squint after stepping out into the full summer sun. However, if I close one eye entirely, I can keep the other open without pain. This seems odd. Naively, one would assume the pain results from too much light entering the eye and doing some sort of damage to the interior, but if this were true, closing one eye would have no effect on the other. Does the fact that it does imply the discomfort is actually related to (e.g.) the sum-total of information reaching the optic chiasma?

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  • $\begingroup$ Not an answer but an addition to your question. Might help to achieve better results. As far as I can remember I have always closed my left eye in bright light. I am right eye dominant. This is in Indiana which is not extraordinarily high in UV light. I went to Guam recently and I found I could not open either eye without extreme discomfort. Guam is notably high in the UV spectrum. Sunglasses were a must at all times. I am Caucasian with blue eyes. In the latitude of Indiana I have not had extreme discomfort as in Guam but have had to close my left eye more than enough. As a Biologist, I hope $\endgroup$ – Guru Jul 11 '17 at 0:26
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    $\begingroup$ I do not think that there's any scientific reasons why, but it is like a reflex. Your brain knows we do not enjoy bright light in the morning, especially when the eyes weren't open for a long mather of time. It is why peeking slowly to give time to your iris to get adapted to the strong light. Some people open one eye at the time, some people opens both of them and blinks repeatedly. $\endgroup$ – Jade Hamelin St-sauveur Aug 29 '17 at 15:31
  • $\begingroup$ I thought of this same question today. Wish there was an answer! $\endgroup$ – NobleUplift Aug 30 '17 at 17:42
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A couple of factors play into this. First, you're halving the number of nociceptors that are signaling the brain. Second, there is a psychosomatic effect. Your brain continuously combines the visual data from both eyes to form one image. With one eye closed, your brain combines the brightness of both inputs to form an image that is roughly half as bright as reality. As a result, your brain not only ignores a portion of the nociceptor signals from the open eye, but it also doesn't assume the presence of pain like it normally would.

I've no publicly accessible sources to cite, as this is something I learned in my EMT class. Someone actually asked your same question in class

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This happens to me as well. Complete guess (and probably somewhat of a poor answer) but I think it has something to do with focusing problems (similar to an extreme astigmatism) jerking the eye muscles around.

Closing 1 eye removes the need for a coordinated focus, eliminating the problem.

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your right eye is dominant making it a reflex to close the other which in this case is your right eye which is the "Weaker" one

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  • $\begingroup$ Just A guess Sorry :( $\endgroup$ – Bryan Vallejo Sep 19 '17 at 19:04
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    $\begingroup$ If you could add some references, and expound, that would be good :) $\endgroup$ – L.B. Sep 19 '17 at 19:15

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