Why does squinting help you see better?

http://digg.com/health/How_Does_Squinting_Help_Us_See

http://www.livescience.com/mysteries/070102_squint.html

No, squinting allows less light into your eyes. The less light going into your eyes makes your pupils expand and that allows you to see more. Go into the bathroom and turn the lights out. Look into the mirror and turn the lights on and you’ll see your pupils quickly contract because while it was dark your eyes were at their largest diameter.

@QC
Sorry to disagree, but as this article demonstrates, visual acuity (sharpness) is greater when the pupil is smaller. This is why many opthalmologists discourage patients from driving after having their eyes dialated.

The source syz cites is correct in explaining that the pressure of squinting the eyes changes the shape of the eye’s lens ever so slightly. The internal muscles of the eye are constantly tugging on the lens to stretch it into different shapes for focussing on near or far objects. The second citation states that this isn’t a factor in how the normal eye focuses but, in people with astigmatism, the lens is not properly shaped and the eye’s internel muscles can never produce a single point of focus. Squinting can compensate for the out-of-round lens by forcing it into a more rounded shape using the external muscles.

I should have squinted as I typed…sorry for all the typos

Hey, I have myopia and astigmatism and with computer glasses, regular glasses or squinting, I had absolutely no problems reading (and understanding your answer.)

It’s fantastic that you did a google search and came up with a website that sells computers to give you your research, but as your “source” goes on to discuss:
“There is a relationship between visual acuity and pupil size, but Figure 15 clearly shows that the relationship between light level and pupil size is of importance only for low light levels. In other words, there is a point beyond which increasing the light levels does not improve visual acuity due to pupil size.”

@QC
Yes, it’s amazing, isn’t it, how much information you can get through a simple Google search, especially on an optical principle that’s so well documented. In addition to that nasty, commercially tainted source I cited, you also find scads of scholarly articles and print references, all curiously saying the same thing as my unworthy source.

The consensus seems to be that large pupil diameter produces optical aberrations in the eye that reduce visual acuity. Extremely small diameters (on the order of <1.5mm) lose some acuity due to diffraction (not due to insufficient light reaching the retina) in non-myopic eyes, though they can improve acuity in myopic eyes.

If you can find information to support your assertion that dilating the pupils improves the optical performance of the eye by allowing it to “see more”, I’d like to see that.

@Harp: wearing my bifocals and squinting, I can still understand you. And also true that when I have my pupils dilated at Ophthamologist’s, I can’t focus for several hours. Of course, that is empirical and not documented.

like a camera lens it increases the f stop, meaning less light comes in, but it comes in at a smaller angle, thus giving you more depth of field, which to your brain makes it seem like everything is more in focus.

if I could scan my anatomy book I would but I don’t own a scanner.

A camera does not have an irregular cornea or a lens that is slightly and permanently misplaced in the same place. Blurriness in the human eye (or sharpness) has little to do with light-gathering power. I can read finer print in a stronger light by either wearing my glasses or squinting.

that is because light is making your eye close some, like a camera lowers its shutter, your eye is limiting how much light in like an aperature, thus the more light, the less the depth of field, making everything seem sharper, but in fact a larger range is in focus, whereas the opposite happens in dim light, your eye opens wide and tries to gather more light, and you get a larger depth of field, which makes focusing harder and takes longer, which is why they say don’t read in dim light otherwise it will work your muscles to much and you’ll get a bad headache