# Pupil contraction. **URL:** \ **Category:** Factual Questions\ **Created:** [February 3, 2012, 3:10am UTC](https://boards.straightdope.com/t/pupil-contraction/611615 "2012-02-03T03:10:34Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Mewl\_Dear](https://avatars.discourse-cdn.com/v4/letter/m/d6d6ee/32.png) [@Mewl\_Dear](https://boards.straightdope.com/u/Mewl_Dear)\ **Post date:** [February 3, 2012, 3:10am UTC](https://boards.straightdope.com/t/pupil-contraction/611615/1 "2012-02-03T03:10:34Z")
A guy told me today that if you close one eye and shine a light in the other both pupils will contract. No matter how many times I try this in front of the mirror, I can not focus quick enough. Fascinating, if true. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [February 3, 2012, 3:16am UTC](https://boards.straightdope.com/t/pupil-contraction/611615/2 "2012-02-03T03:16:09Z")
According to Mythbusters, pirates wore eyepatches to keep one eye ready for vision in the dark when they went below in ships they were plundering. Their test proved some basis for this. I don’t know if it was due to pupil dilation though. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [February 3, 2012, 3:42am UTC](https://boards.straightdope.com/t/pupil-contraction/611615/3 "2012-02-03T03:42:52Z")
Definitely true. And, it can be exploited to help determine the site of the problem when it involves the nerves controlling the pupil (the bane of many med students). For those interested in such things look [here](http://www.cybersight.org/bins/volume_page.asp?cid=1-13-161-987) for a nice web page link or [here](http://www.youtube.com/watch?v=HSYo7LhfV3A) for a video. I can (try to) answer any questions you have but can’t do any better than the links for an intro. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [February 3, 2012, 3:49am UTC](https://boards.straightdope.com/t/pupil-contraction/611615/4 "2012-02-03T03:49:24Z")
> [@TriPolar](#): > > According to Mythbusters, pirates wore eyepatches to keep one eye ready for vision in the dark when they went below in ships they were plundering. Their test proved some basis for this. I don’t know if it was due to pupil dilation though. Pupils respond very quickly to change in light, but [chemicals in the rods are slower to react](http://health.howstuffworks.com/human-body/systems/eye/eyes-adjust-darkness.htm), and this is why it takes a while to get used to the dark (and why covering one eye keeps that eye at the ready for darkness). ---
**Author:** ![picunurse](https://avatars.discourse-cdn.com/v4/letter/p/7bcc69/32.png) [@picunurse](https://boards.straightdope.com/u/picunurse)\ **Post date:** [February 3, 2012, 6:24am UTC](https://boards.straightdope.com/t/pupil-contraction/611615/5 "2012-02-03T06:24:13Z")
Yes, in a normal individual, both pupils react to light together. In neurological injury, one test is to shine a light in one eye and check pupil response in the other. This test is mostly to check for injury to the optic nerve. ---
**Author:** ![MLS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MLS](https://boards.straightdope.com/u/MLS)\ **Post date:** [February 3, 2012, 6:37pm UTC](https://boards.straightdope.com/t/pupil-contraction/611615/6 "2012-02-03T18:37:15Z")
On an eclipse-viewing trip 2 years ago, a few members of our party put eye-patches over one eye and then switched it to the other eye at totality. They said it was really amazing. This also resulted in lots of pirate jokes, especially since the eclipse viewing was on a boat in the south Pacific. ---
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [February 3, 2012, 6:45pm UTC](https://boards.straightdope.com/t/pupil-contraction/611615/7 "2012-02-03T18:45:28Z")
> [@TriPolar](#): > > According to Mythbusters, pirates wore eyepatches to keep one eye ready for vision in the dark when they went below in ships they were plundering… Is this actually true? I assume Mythbusters was verifying whether or not it worked, but is this really the story behind the ubiquitous pirate eye patch? ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [February 3, 2012, 9:31pm UTC](https://boards.straightdope.com/t/pupil-contraction/611615/8 "2012-02-03T21:31:22Z")
I think Mythbusters said that it could be _possible_ in that it works, but they were not ever claiming that most pirates had two good eyes and only wore patches for that reason. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [February 3, 2012, 9:43pm UTC](https://boards.straightdope.com/t/pupil-contraction/611615/9 "2012-02-03T21:43:01Z")
> [@thelurkinghorror](#): > > I think Mythbusters said that it could be _possible_ in that it works, but they were not ever claiming that most pirates had two good eyes and only wore patches for that reason. I don’t recall, but they may have declared it ‘plausible’. ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [February 3, 2012, 10:57pm UTC](https://boards.straightdope.com/t/pupil-contraction/611615/10 "2012-02-03T22:57:50Z")
> [@TriPolar](#): > > I don’t recall, but they may have declared it ‘plausible’. My recollection too, but didn’t want to say for certain. To the Internets! [Yep](http://en.wikipedia.org/wiki/MythBusters_%282007_season%29#Episode_71_.E2.80.93_.22Pirate_Special.22).