Why can I see out of my eyeglasses better when I tilt my head back?

June 9, 2015 12:01 PM

I have a new pair of glasses that I like just fine. Even though the prescription is a little stronger in one eye than that of my previous pair, I've noticed that I can actually see some things better if I tilt my head back and look through my glasses at a slight angle or through the bottom of the lens. What gives?

Is this an issue with pupil distance, lens curvature, or something else? I don't have astigmatism (that I know of).

Here are the details:

-I'm nearsighted (-1.50 L, -2.50 R) and can see ~20/20 with corrective lenses.
-If there's something really far away that I can't quite read, I can tilt my head back and look through the bottom part of my lens to focus better. I've been able to do this with both my old pair and my new pair of glasses.
-I ordered the new glasses online from a company I've used for years.
-The new glasses have slightly larger lenses than the previous pair.

posted by yellowcandy to Health & Fitness (7 answers total)

Best answer: Often the optical center of your lens is somewhat below your pupil when you look forward.

The optical center (which is the thinnest part of your lens, not necessarily the center of your frames) gives the clearest vision. Are you sure you're looking through the lower half? Maybe you are just looking through the center?
posted by fritley at 12:13 PM on June 9, 2015

I think it's the same effect as the phenomenon that peering through a small hole gives you a sharper images: http://pinhole.stanford.edu/howitworks/size.htm In the pinhole effect, the angle of the light cone that reaches your eye from a faraway object is made smaller by having to pass through the small hole. This makes the image sharper. In your case, when you tilt you head, light hits your lenses at an obtuse angle, so more rays gets refracted on your glasses, making the angle of the light cone that reaches your eyes smaller as well.
posted by tecg at 12:20 PM on June 9, 2015

Do you get the same results from lifting your glasses up a little bit? Because it sounds like they're just sitting too low on your face. Next time you get new glasses, talk to them about this. Or you could just get a bigger nose.
posted by aubilenon at 12:37 PM on June 9, 2015 [1 favorite]

Best answer: I'm guessing your lens' optical center is not aligned with your eyes, or your prescription's out of date.

I have a large head and I had a hard time finding a good frame, and even then lense center doesn't align with my eyes. Optician was supposed to mark the center of your eye on the lens so the lens makers can make offset if any.
posted by kschang at 12:38 PM on June 9, 2015

Best answer: Saw this post and also immediately thought "optical center."

A good optician will measure this (different than your prescription) when fitting you for glasses by both having you look into a device and also having you put on the frames and marking the lenses with a pen.

Maybe some retailers have found ways to address this, but my understanding is that this unfortunately tends to be a trade-off with ordering glasses online.
posted by suprenant at 2:06 PM on June 9, 2015 [1 favorite]

Have you had them adjusted since receiving them? I always bring my ordered-online glasses in to my optometrist's office for fitting/adjustment after I receive them. I'm not going to apologize for buying several pairs of glasses for the price of one of theirs, and I offer to pay for the adjustments, but they don't charge for that. (Some places I've been for adjustments do charge, but it's a nominal fee. And hey, I pay full fare on the exams with all the trimmings, every year.)

Anyway, tiny adjustments can make a huge difference, so make sure you've got those things on straight. The two pairs I got in my last order were unwearable until I got them tweaked. This is something you might have to do more than once over the course of wearing a pair of glasses.
posted by asperity at 3:21 PM on June 9, 2015

I use to do that as my eyesight got worse, lifting them to look through the bottom, that is. My doctor told me the script was stronger there. Notably did that at around 12 and mentioned it to my doctor, just got newer glasses for my deteriorating eyesight until I eventual got surgery (glasses were very expensive, contacts painful, severe astigmatism, very bad vision, so even though it was expensive at the time, the cost was negligible comparatively.)
posted by provoliminal at 11:58 AM on June 10, 2015