Lens Quality

[edKENdance]

As a layman(er..person) I was wondering about the differences in lens quality from one manufacturer to the next. I have been led to believe that glass is of a higher optical quality than CR or PolyCarb. As long as a lens is of optical quality is it just a matter of aesthetics after that or are there actual tests that can prove one lens is "nicer" to look through then another. Also, cheap drugstore readers and sunglasses are obviously not of optical quality which one can easily tell due to the distortions in the lenses. Another question is what are these lenses made of and how is a manufacturer of lens material able to offer low grade distorted lenses to the public?

[Homer]

Interesting name, Maybe it is Ed-can-dance?
Also interesting questions to which you should be able to find very complicated, technical and varried answers in these forums.

To paraphrase another saying, If we have 2 opticians we are likely to have 3 opinions.

I have doubts at to your complete novis position due to some things your said, but will answer as if you are.

First, each major manufacturer is sure to say that their lenses are of the highest quality. The defenition of what exactly constitutes quality is not very well stated.

We do have the American National Standards Institute which attempts to describe some of the generally accepted criteria for the prescription eyeglass industry. Ready-made reading glasses and some aspects of sunwear do not fall under these standards. By the way these are volunteer standards, not law.

When your say obvious distortions, what do you mean exactly? What is your criteria?

As in any industry, there are those who shortcut the system in one form or another in order to get market share, usually at the lower end.
It could be the softness of the material, or hardness of coatings, or integrity of the surface or consistancy of the material or the durability of the product over time (such as it's response to UV light).

The end result is that none of them will blind you and there is a 90% chance that if your prescription was measured, fabricated and fitted correctly that you would not be able to tell much difference between one major manufacturers product and another. Kinda like going to Grandma's house in a Chyrsler, GM or Ford product of the same type and features - you'd still get to Grandma's in style and comfort.

There are great products out there with great features and benefits that can be very sophisticated and need to be explained to you by an optician you can trust. If however you don't trust anyone and you want to play doctor, then I don't know of an optician that can help you very much.

I know there are at least a dozen people on this board who will be glad to respond to your specific questions and can give you more information than you want to know. We love doing that.

Hope you find a knowledgable, professional optician who will listen to your concerns and answer your questions.

[John R]

Well yes glass does have a higher optical quailty than its "plastic" counter parts. But it does have its down side ie. weight. Don't think that joe public would be able to notice much if any diffrence though in optical quality.
As to the distortions in cheap sunspecs its more likly to be down to the lenses being to tighter fit in the frame, or some would say you get what you pay for...

------------------
Every day a grind
Every week a bind
www.iooi.co.uk

[This message has been edited by john r (edited 03-11-2001).]

[chip anderson]

No one seems to recognise that optical quality can vary from lens to lens in the same brand and surfaced by the same lab. You need not only brand/design/manufacturer assureance, you also need a good (note that word) optician to inspect the things for aberration and surface defects as well as power and center compliance.

Chip (Who used to think he was a good Optician).

[JRS]

Chip, I would think that if you are having to spend time looking for aberations, surface quality, thickness compliance, etc. - you need to switch labs. I would expect those to not be an issue when I receive work. Certainly I would verify power, pd's, and the like, but not those others. I might have to get that (post-inspect detail) if a patient has a problem, but not on every job.

[Jim G]

Geez, I gotta start with the old rejoinder, "Don't ask a q. unless you're ready for the answer."

All powered lens systems exhibit some level of distortion away from the center of the lens. The primary factors are: lens design, lens material and power.

Optical designers spend years and untold computer power to try to design lenses that minimize distortions. Typically tho, as you decrease one, you increase another.

Lens materials exhibit different abilities to refract (bend) light. We use a term, Abbe, to note that function. Lenses with lower Abbe values "bend" the light more BUT, as a result, increase the level of "chromatic aberrations" as seen as
colo(u)r rings near the edge of the lens. You might ask, why even consider a lens material that would do that? The trade-off is a thinner and typically lighter lens. And, users quickly get used to the colors.

Lastly, power. Simply stated, the greater the power, the more aberrations.

Whoops, forgot that we, the processing lab, can take all the good intentions of designers, fabricators and dispensors and screw it up royally...hopefully not very often tho.

Cheap lenses are typically made of sheet acetate or "sagged" plastic where a flat sheet of plastic is placed over a form and heated (or pressed) 'til it assumes the shape of the form. Adequate for casual vision but certainly not an optical product.