Over in this thread: http://boards.straightdope.com/sdmb/showthread.php?postid=2326512#post2326512
DanTheMan mentions that smaller eyeglass lenses may actually be better for your eyes than larger lenses.
Having worn glasses for twenty years now, I can’t imagine why smaller lenses would be better. I prefer larger lenses so that I have more space to move my eyes (a wider field of view.)
Are there any opticians out there with an enlightening word or two?
Well, in my case (extreme myopia), smaller lenses mean that the edges aren’t as thick (even with the new superlightweight plastic lenses) as they would be with big ones. As it is, I can’t get frames with very thin edges, because they won’t hold my lenses securely.
This still doesn’t mean that it’s better for my eyes, however – it’s just an aesthetic advantage.
As Scarlett says, the lenses get thicker toward the edge. That means that toward the edge you’ll experience more distortion and chromatic aberration.
For example, I have a pretty strong prescription (myopia) and if I look specificially out of the sides of my glasses, I can see that lines that should be straight are, in fact, curved. Now, when I’m looking straight ahead, I don’t notice at all because my brain is used to the distortion, and straight lines seen out of the corner of my eye are interpreted by my brain as straight, even if my eyes see them as curved.
Bizarre fact: they did this experiment one time wheret they put glasses on people that inverted the image! They were seeing the world upside-down! But after a few days of wearing the glasses all the time, their brains adjusted, and they were seeng right-side up again. (I am not making this up. Cite: Stratton G. M. (1897), Vision without Inversion of the Retinal Image, Psychological Review IV, No. 5.)
Gives ya new respect for yer think-meat, don’t it?
Anyway, if I look at the Moon out of the corner of my glasses, it has a stripe of blue down one side and a stripe of orange down the other–that’s chromatic aberration. Can’t adjust to that, but it’s only at the very edges, and I don’t notice it much.
I don’t think that that is it. I have my new glasses now, and they have noticeably less distortion and less chromatic abberation towards the edges. The lenses are larger by five or six millimeters of diameter, and the glass is of a lower index of refraction.
I think they’re always developing new materials for lenses. For example, I got new lenses a couple of months ago, and they were just coming out with some material that allowed graduated lenses to be smaller than before.
Podkayne writes:
> Bizarre fact: they did this experiment one time wheret they put
> glasses on people that inverted the image! They were seeing
> the world upside-down! But after a few days of wearing the
> glasses all the time, their brains adjusted, and they were
> seeng right-side up again. (I am not making this up. Cite:
> Stratton G. M. (1897), Vision without Inversion of the Retinal
> Image, Psychological Review IV, No. 5.)
Well, no, actually, that’s a misunderstanding of Stratton’s experiment. Here’s the nearest I can quickly find on the net to a description of what he did:
http://wearcam.org/tetherless/node4.html
First, Stratton only did this experiment to himself. Second, he found that he was able to adjust to it and walk around and handle things normally after a while. He did not find that the image flipped over and became right-side-up. He just became accustomed to it being upside-down, so it didn’t matter to him. Are there any experts in the psychology of optics out there? Surely this experiment has been done again in the past 105 years. What was the result?
Actually, no. When seen throught the center of your lenses, straight lines should not be distorted.
This is what got me started on this thread. The distortion varies depending on where you look through the lens, and I got my optician to do some things with the lenses that minimize the distortion so that my brain has less crap to correct (which it doesn’t do so well, anyways. I can’t shoot pool worth a damn because of it.) A statement I made about larger lenses in conjunction with glass with a lower index of refraction prompted DanTheMan’s comment on smaller lenses being better for your eyes.
As far as I remember from a childhood fascination with telescopes, larger lenses with lower curvature distort less and cause less chromatic distortion.
So, any opthamologists out there?
I’ll have to do a little more research on this. Last year, we received some instruction in the basics of optics from the former science officer of the Clinton administration. Our instructor (who’s affiliated with the University of Rochester) had noted that some people in the room had glasses with smallish lenses, and he said that he was glad to see those lenses coming more into style, as the smaller lenses were actually better for the eyes than the large ones that have been in style for a while.
I’ll have to check with him again to make sure I didn’t misinterpret him or that I am misremembering.
[Paul Lynde]
Well, it may be abused, but it’s certainly not neglected!
[/Paul Lynde]
Here’s my contact’s response:
And this is coming from someone who’s published numerous papers on the subject. So it’s an aesthetic issue, but it’s also a field-of-view issue.