I have a sweater that is 40% acrylic and 60% polyester. It looks as if it was knitted, i.e. it has little tiny holes in between the threads (see pictures).

 

 

I'm shortsighted, and when I take off my glasses and put the sweater in front of the eyes, I can see much more clearly than I can without glasses. It's not as clear as when I do have my glasses, and the threads get in the way, but there is a marked difference. I'm guessing light gets diverged like going through a corrective lens, but all it does here is pass through small, physical holes. Why does my vision get clearer when I wear my sweater in front of my eyes?

Pinholes act like corrective lenses — the small aperture filters off-axis rays, which are the ones that cause the most problems in trying to focus properly if you have bad vision.

 

http://www.myopia.org/pinholes.htm

The pinhole in front of your eye makes your eye into a pinhole camera

I do the same thing by folding my forefinger, leaving only a small hole to look through.

The pinhole in front of your eye makes your eye into a pinhole camera

I do the same thing by folding my forefinger, leaving only a small hole to look through.

 

I do that too when I'm attending a lecture, and forgot my glasses at home.