Glasses Urban Legend

[jimbotheclown]

I have been told by many of my friends that a person with good vision can get a good guage of a visually handicapped person's vision simply by putting on their glasses. I have learned from this glorious q&a forum to question everything, so I now present it to my fellow Teeming Millions. Is there any truth to this, or is it just another hare-brained idea created by some equally moronic person?

[FatBaldGuy]

No, if the person was nearsighted, then a person with normal vision would perceive things from a farsighted perspective, due to the correction. Think of it numerically as points on a line. If the person with glasses is normally at -100, then a +100 correction would bring that person's vision to normal. However a person already at zero would put on the glasses, and their vision would appear as +100.

Not a very scientific explanation, but you get the general idea.

[kunilou]

Do you mean the person with good vision can figure out how bad the other person's vision is? Or do you mean that a person with good vision can get an idea of what it's like to have bad eyesight by wearing the other person's glasses?

[CrazyCatLady]

Well, if I accidentally put on my glasses when my contacts are in (I was bad about that when I first got contacts, some habits are hard to break) everything is blurry and out of focus. However, it's not the same sort of blurry and out of focus that things are without lenses of any type, if that makes any sense. I think you can get a feel for how distorted someone's vision is, and what it's like to go around like that, but you don't get a feel for what it's really like.

Essentially, FBG, is oversimplifying a bit but has the gist of it right.

[sailor]

Originally posted by jimbotheclown
Is there any truth to this, or is it just another hare-brained idea created by some equally moronic person?

The correct answer is (b) as you can easily test for yourself. Ask a young person with good eyesight to wear the glasses of a nearsighted person with, say 1 to 2 diopters. This person can still see perfectly well as his vision will adapt. Some people need to do a little testing before they invent "new" theories.

[Joe Random]

I'm nearsighted, and I've found that the best way for anyone to see things the way I do (without glasses) is the following:

Close one eye. Or cover it if you're one of those rare people who have difficulty closing just one eye at a time. Next, focus your open eye as close to you as you can. It might help to hold something very close to your face on focus on it, then move it out of the way while maintaining the same focus. Everything at any appreciable distance should be all blurry, now.

If I do this with my glasses on, and then simultaneously remove my glasses and return my focus to normal, I can barely tell the difference. The only thing that changes is the astigmatism, which can't easily be simulated.

[Captain Lance Murdoch]

Sorry sailor, but I have to disagree. A person with good vision (or with not-so-good vision) can gauge another person's eyesight by looking through their glasses. I worked in the industry for a couple of years and I did it all the time. I could tell a person's Rx within a half diopter nearly every time.

[zuma]

Obviously a person with normal vision can determine how bad the eyesight of someone with glasses is by viewing objects through the glasses.

The worse the vision, the more distorted the view to the normal-eyed viewer. I'd think that they would also be able to tell whether the glasses person was near-sighted or far-sighted

[FatBaldGuy]

Yes, rogzilla and zuma, you can definitely get a good idea of how much correction is involved, but when A puts on B's glasses, A does not see things the same as B would see uncorrected. I think that's what the OP was asking.

[Agback]

Originally posted by jimbotheclown
I have been told by many of my friends that a person with good vision can get a good guage of a visually handicapped person's vision simply by putting on their glasses. I have learned from this glorious q&a forum to question everything, so I now present it to my fellow Teeming Millions. Is there any truth to this, or is it just another hare-brained idea created by some equally moronic person?

This can at best give an indication of the extent of their refractive error (what glasses correct). It won't, of course, tell you anything about any cataract, retinal pathology, or neurological problem in the visual or perceptual system.

Another point to note is that in many places it is customary to under-prescribe: to give people glasses not quite strong enough to correct their refractive error. The ostensible reason is to 'train' the eye to prevent deterioration, but so far as I am aware the evidence is that it makes things worse, especially in children (the first proper study was done last year or the year before).

And bear in mind that the negative-dioptre glasses of a person who is shortsighted will make a person with normal vision longsighted, and that the positive-dioptre glasses of a person who is long-sighted will make a person with normal sight short-sighted. So even leaving out questions of whether -1.0 dioptre refractive error is "equally blind" with +1.0 dioptre refractive error, being short-sighted is not like being long-sighted.

Regards,


Agback (not an optometrist or ophthalmologist)