Edit: My thought process is that using one eye would still cause enough uncomfortable sensations that closing / squinting both eyes is the only viable option but apparently not. One eye is completely normal and painless.
This happened to me when I was driving the other day and I was worried I’d have to pull over on the highway, but when I closed one eye I was able to see with no pain sensation whatsoever with roughly the same amount of light radiation entering my 👁.
I know it’s technically less light for my brain to process, less intense on the nerve signals firing but I couldn’t intuitively get to the bottom of this because the common person might assume having one eye open could be worse?
In: Physics
Yoir optic nerves absorb light and transmit that to your brain for processing. If you close one and squint the other, you reduce the amount of light, thus processing your brain needs to do. It’s a reflex from the brain processing the data. Same as when something is flying at your face and you close your eyes and look away
You have a blink reflex when exposed to bright light. Ideally, you’re exposed to a light that’s too bright and you squint or close your eyes to prevent any damage.
You might ask, “Surely only closing one eye shouldn’t help, since the open eye could still be damaged, right?” And you’d be absolutely correct. This is a glitch of the human nervous system.
Essentially, this glitch occurs because your brain registers bright light by adding together the amount of light received in both eyes. If one eye is closed, that eye is receiving the same amount of light, but the brain is only registering half of the original amount.
Fun fact, some people (Ze Frank is a notable example) don’t have this glitch. You can (but don’t, it’s not good for your eyes) test this by shining a light in one of your eyes, blocking the light from getting to the other eye, and watching to see if your non-lit pupil constricts. Normal people’s pupils will both constrict if one eye is exposed to bright light. In the case of Ze Frank and others, only the pupil receiving the light will constrict.
Your brain combines the things each eye sees and uses information from both eyes to form a single “image”. You can test this real quick by closing one eye and leaving the other open and then switching which eye is closed. If you look at an object you should see it “move” if you do this fast enough.
If you tried to walk around like this for a day you should notice you will have problems with knowing how close objects really are and balance.
This becomes an actually helpful thing if you’re in a situation where the combined “image” is too much for your brain( like too much brightness too fast ) and closing one eye does reduce the brightness your brain “sees” because it’s less “information”.
Of course this isn’t really reducing the brightness the remaining opened eye is observing but your brain determines what you “feel” and it let’s you know this is better than both eyes opened.
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The optical nerves that links each eye to the brain forms an “X” because the left eye’s nerve connects to the right side of the brain and vice versa.
When both eyes see bright light, a lot of signal goes through the nerves and it takes a few seconds for our eyes to adjust to send less signal. These signals meet at the center of the “X” where the nerves cross over, called the optic chiasm. Too much nerve signal in one region can be interpreted as pain by the brain.
Closing one eye helps reduce the overall amount of signal below a pain-causing level as our eyes adjust to the bright surroundings.
Compressive lesions on this optic chiasm can cause photophobia (sensitivity to light) because it’s worsening the “traffic jam” of nerve signals: https://pubmed.ncbi.nlm.nih.gov/11937897/
Theorizing here.
Unless you turn your head to directly face the sun, which would be uncomfortable to do, one eye will be somewhat shielded from the sun by our brow and nose.
I dont know about you, but the eye I close is the sun side one, and I use my face as shade for the other.
I used to stare at the sun as a kid and see how long I could hold the stare….but I’m sure that’s not why I wear glasses, no not at all
I think this explains why I close one eye to look at my phone screen when I’m too drunk and in the dark because the screen too bright? It’s so much easier looking at it with one eye.
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