Why is there color distortion on my glasses?

August 29, 2005 10:13 AM

Why is there color distortion on my glasses?

I recently got a new pair of glasses and I'm experiencing something I haven't before. As I move away from my center of vision, I get a haze along straight edges. Its most noticeable in the horizontal direction, appearing as a blue line when moving from dark to light surfaces and a yellow line when moving from light to dark surfaces. It's most prominent on the edge of my lenses but I start to notice it pretty soon after my eyes look to the side. I asked the store about it and they said it was just normal distorion on the edge of the lens, but I'm seeing the colors constantly and obviously its enough to bother me. I'm gonna go back and ask again but just wanted to know if this really is common.

posted by trillion to clothing, beauty, & fashion (13 comments total)

You mean there are glasses where you don't get color fringes? I've always had that with my glasses, for as long as I can remember, which is something like thirty years.
posted by kindall at 10:20 AM on August 29, 2005

It's chromatic aberration you're seeing. Nearly all single-element lenses suffer from it. Was your previous pair glass, and these plastic, or vice versa?
posted by scruss at 10:37 AM on August 29, 2005

Are your glasses frameless or partially frameless? With polished edges?
posted by Thorzdad at 10:37 AM on August 29, 2005

This is my fourth pair of glasses (all glass lenses) but the first that is partially frameless. The edges are not polished, they are opaque. Its starting to seem like this is a normal thing.
posted by trillion at 10:42 AM on August 29, 2005

I don't exactly know what affects this phenomenon, but I've noticed that the thicker the lenses are, the stronger the effect seems to be. I remember it getting worse as I got glasses with stronger and stronger prescriptions.

I'm not sure if the correlation is tied to thickness or strength though; I remember my last pair having a worse effect than my current one, and they're basically the same strength, but my current one had a thinning treatment done on it, so that may be it.

But I don't remember ever being free of this, except when I wore contacts for a time. I mostly notice it in extreme cases, like at the edge of the fluos on the ceiling at work, lights in the street at night, etc. If you get it at the edges of a computer monitor in a bright room, for example, I would say that's excessive and maybe the glasses are defective somehow? But I'm no optometrist.
posted by splice at 10:46 AM on August 29, 2005

i always thought that it was because my lenses were UV coated
posted by spunkster at 11:09 AM on August 29, 2005

I've noticed this with my glasses also, particularly when looking at two fairly pure colored lights that are close together, like in an Atari game, or on the TV screen showing scores at a bowling alley, something with expanses of solid colors.

Anyway, look at the screen, then shift your head a little to the left or right. The colors should move, of course, but at different rates. Blues and reds will move different distances, for instance, resulting in gaps between what are really adjacent blocks.

I've always thought this was due to the fact that different colors of light are bent at different angles in a prism, which is what your glasses are acting as. This would be most pronounced at the edges of your vision.

If someone has a better explanation of the physics behind this, I'd love to hear it.
posted by odinsdream at 11:13 AM on August 29, 2005

Er, scruss has it covered.
posted by odinsdream at 11:14 AM on August 29, 2005

I don't exactly know what affects this phenomenon, but I've noticed that the thicker the lenses are, the stronger the effect seems to be.

Basically, the stronger your prescription is, the wider the edge of the lenses need to be relative to the center of the lenses. This means that the outer regions of the lens would look like narrow prisms in cross-section.

If it's bothering you, you might try switching to lenses made of high-index plastic, which definitely require less change in thickness over the range of the lens, and might also have less change in index of refraction over the range of visible light. I have plastic lenses for a prescription around -6 diopters, but I only rarely notice chromatic aberration.

(When I do, it's usually at rock concerts, where I play around with looking at the purple lights through the edge of my lenses & splitting them into red & blue. This has been known to keep me sane during the boring parts.)
posted by Johnny Assay at 11:16 AM on August 29, 2005

And if it's any consolation, I get the same effect from the plastic lens implants I got after cataract surgery. Drives me nuts, especially when I'm trying to write on white paper, and I can't even take my glasses off.
posted by sneebler at 5:07 PM on August 29, 2005

I have the same thing with my glasses, for as long as I can recall, so this is over the years and many pairs. I always chalked it up to a trick of light refraction? and my very strong prescription.
posted by Savannah at 5:49 PM on August 29, 2005

Buyer beware: I suffered from this same irritation, and last time I got new lenses I sprung for the "high index." I still have CA. Slightly less, but still very annoying.

I used to see no CA whatsoever, although it was a few prescriptions ago, it was also with lenses from a very highly regarded private eyeglass shop. My insurance-covered specials suck compared to them.

I fear that the high index is to the eyeglass industry what the extended warantee is to the retail business, and the Tru Cote "invisible" protective finish is to car dealers. I'm sure they are slightly, yet measurably better than standard lenses, but not perfect.

Someone with more experience in optics please tell me this is not true. I work in the performing arts, and staring at purple lights is actually a significant part of my life. I would love to see them as just purple, not red and blue.
posted by sol at 7:17 PM on August 29, 2005

The high refraction index lenses are great if your lenses are so thick they drag the frames down your nose, like mine used to be. Back when glasses had to be made of, you know, glass, I had to have serious nose brakes on my spectacles that left these huge red welts on my nose. Their primary benefit, as with plastic lenses in the first place, is in being lighter. Still, if your glasses are light enough to be comfortable already, why pay extra for high-index lenses?
posted by kindall at 7:52 PM on August 29, 2005