What tool did the optometrist use?

March 3, 2009 9:30 AM

What did the optometrist use to make my vision so much better, and how does it work?

Not the fancy bells/whistle machine with all the cool gears and lenses. Before that, he used a simple piece of plastic to block one eye and leave a hole for the other. After testing vision with that, he flipped a second piece of plastic over the hole -- from what I could tell, the second piece was just a thin sheet of opaque plastic with a bunch of small holes in it. No lenses or anything, just little holes.

With that covering my eye, I could see the smaller print much more clearly. How does that work? Does it replicate the eye squinting by reducing visual "noise" or something? I'm fascinated.

posted by Pantengliopoli to health & fitness (9 answers total)

Like a camera lens, the smaller the aperture, the wider the depth of field.

By making the aperture of the iris of your eye as small as a pinhole camera, most everything will be in focus.
posted by tomierna at 9:34 AM on March 3, 2009

That's amazing... I've never really understood depth of field or how it works wrt the aperture.
posted by Pantengliopoli at 9:39 AM on March 3, 2009

Actually, my mother was telling me about these. Pinhole glasses is the googling term you need for further info. Thanks for reminding me to look them up.
posted by lucia__is__dada at 9:47 AM on March 3, 2009

Google pinhole magnifier for more detail.
posted by MrMoonPie at 10:06 AM on March 3, 2009

I can't read anything beyond 1ft without glasses, but if I need to read my alarm dial in the middle of the night, I make a small hole with my fingertips to see through. Then I can read the blur!
posted by cowbellemoo at 10:13 AM on March 3, 2009 [2 favorites]

People instinctively squint their eyes when straining to see something better. Making a slit with your eyelids reduces the aperture of the eye, improving visual acuity.

The optometrist uses the pinhole test to determine the underlying visual acuity of your retina despite refractive problems with your cornea or lens.
posted by JackFlash at 10:45 AM on March 3, 2009

Wow -- that's just fascinating. I had no idea -- thanks everyone. I'll be making little circles with my fingers and staring at stuff for the rest of the day.
posted by Pantengliopoli at 11:04 AM on March 3, 2009 [1 favorite]

Pinhole glasses are also used in the Bates Vision Improvement Method. More info here.
posted by willmize at 11:37 AM on March 3, 2009

JackFlash is correct. The tiny hole means you're using a much smaller bit of your cornea. It's sort of like if you look at a fun house mirror from ten feet away the mirror makes you look really tall or really fat, but if you look at the mirror from an inch away the bit you can see isn't very distorted.
posted by paulg at 6:55 PM on March 3, 2009