Eyemovement and glasses

August 18, 2005 8:10 PM

A question about eyeglasses, and range of eye movement.

I have worn glasses since I was 2, so you'd think I'd know the answer to this.
Is there a range of vision one should expect with glasses. That is if looking straight ahead is 0,0 should there be a certain amount of +/-X and +/- Y that does not distort?

Now I know there are some factors such as prescription strength, frame size/shape, and eye problem.
For me I am far sighted with an astigmatism, and a higher then average Rx. Add to that bifocals. I just picked up my new specs which are quite different from my frames that I have worn for the past 6 years.
Before those I wore contacts for 10 years which gave me the freedom to look without turning my head (obviously always seeing through 0,0). My glasses after the contacts went through 3 pairs of lenses, but I could move my eyes and only at the edges would vision distort
I have gone from these (49mm wide) to these (52mm wide).
I know there needs to be time for adjustment, but there is a very pronounced difference with eye movement without a dramatic increase in Rx.
Now this is just a curiosity question not a true concern.

posted by sailormouth to science & nature (5 comments total)

There will definitely be a dramatic change moving from contact lenses to glasses. There's no way to avoid it. Most lenses (if well made) are not straight and have a slight curve on the edges. This is done to accommodate the movement of the eyeball in order to minimize any possible distortion made when focusing on something that is not directly in front of you.

However, due to the fact that lenses (for glasses) are not directly on your eyeball there is no way to account for all movement and there will definitely be an adjustment period. I've heard of certain types of lenses and frames that will minimize this impact, but I've never really looked into them to much. Contact lenses have always caused me more problems then they're worth, so I'm not, by any mean, an expert.
posted by purephase at 9:52 PM on August 18, 2005

A few years ago I went from the 'roundish' large lenses to a frameless quite short (in height) glasses. I had quite a lot of problems adjusting and found that I had difficulty focussing as well as I had previously. I returned to the optometrist on a number of occasions and it was suggested that the point at which they centre the vision correction - that is, the usual midpoint through which I mostly look - was placed quite differently because of the new height of the glasses (which, by looking at your 2 pairs of glasses, doesn't really look to be a similar change, but the reasonably similar shape of each pair of glasses may have little bearing).

So perhaps when they were measuring your eye with that funny little ruler they use, they calculated the centre a little incorrectly - in my case they redid the lenses for free and although I ultimately walked away with less than 100% satisfactory vision, it of course improved over time with prolonged use. That's the only thing I can suggest - ask the optometrist to remeasure and take your old pair of glasses with you as well - they can identify the centre in those and compare that to what they've put in your new specs. (I've also been wearing glasses a LONG time and have had maybe 50 pairs - this problem I've described here was the first time I'd really had a focussing problem that lasted more than a day or 2.)
posted by peacay at 3:22 AM on August 19, 2005

[Oh I should add that I'm strictly myopic with no astigmatism but your description still sounded familiar - it may not be that, but it's something (where they put the centre) that is easy to check and something that they ought to change if indeed it was the optometrist's misreading/miscalculation/inadvertence.]
posted by peacay at 3:30 AM on August 19, 2005

Normal lenses will seems absolutely panoramic after you have to switch to bi (or tri) focal lenses.
My doc put me in progressive trifocals a couple of years back and, while my vision is clear, the actual area of focus is abysmally narrow. You have this little tunnel of focus and everything outside that tunnel is unfocused. Instead of moving your eyes to the side (as you would with normal lenses) I have to move my entire head to focus on anything to the side.
Very aggavating.
posted by Thorzdad at 6:21 AM on August 19, 2005

There is one more factor. The material the lenses are made of.
The eyeglass salesman ordered a newer material which was supposed to make my lenses even thinner. Do to the new shape/size they were actually thicker (the lab cut the lenses 3 times). To boot this material has a known property which the salesman neglected to either remember or mention - lenses are not panoramic, vision is focused.
The eyeglass shop is eating the cost of those lenses and I am going with the old material.
posted by sailormouth at 4:43 PM on August 29, 2005