Ira Asks: How Are Eyeglasses Made?
IRA FLATOW, host:
This is SCIENCE FRIDAY. I'm Ira Flatow.
You know, some of the most obvious things that we have in life are really difficult to understand, for example, eyeglasses. Take eyeglasses.
I'm wearing a pair of reading glasses right now. Millions, perhaps billions, of pairs of eyeglasses exist around the world. People wear them. But do you have any idea how your eyeglasses are made?
I mean, we were sitting around the office the other day wondering the same things, how these eyeglasses are made, and we really couldn't come up with a decent answer. I mean, glasses aren't really made out of glass anymore, right? They're made out of plastic.
Do you have a little mold for your prescription? Do they pour some molten plastic in there and wait until it dries, or do they grind out a lens out of a big hunk of plastic or something else? And what about fitting it into the frame? How do you make the bifocals? How do you make the progressives, all these things which we don't take for granted. We get these things done. We never find out how they make them.
So this week, we decided that we were going to get that, at least that question answered. So we went to Larry Enright, who is general manager at Perferx Optical Incorporated in Pittsfield, Massachusetts. He joins us by phone. Welcome to SCIENCE FRIDAY, Dr. Enright.
Dr. LARRY ENRIGHT (General Manager, Perferx Optical Inc.): Hi, Ira, thank you.
FLATOW: Can you demystify this for us? What happens when I bring my prescription to the optician, or what happens next? Walk us through the process of what goes on in the laboratory to make a pair of eyeglasses.
Dr. ENRIGHT: Sure. We start with a product that's what we call a lens blank. And by the time we get it, it looks like a big plastic hockey puck.
Now, our manufacturers will, you know, I've seen their process of creating this hockey puck form that we start with, and they'll take, you know, different pellets of material, whether it be polycarbonate or some other plastic resin, and they'll melt it down, and they'll put it into different molds. And the molds have different curves on the lens to help to fabricate the prescription. So when we get the prescription from your doctor's office, we'll take that, put it into our computer system, and it'll, you know, take your numbers.
And we create the prescription by two different curves. The curve in the front of the lens and then the curve in the back of the lens will actually make your prescription.
And so when we get them from our manufacturer, the concave side of the lens, the front of the lens, is already established with a curve. And we do measurements in what's called diopters, something that we've never certainly learned in school or in math class.
And so it's a little funky to that end of it, but basically, like, let's say somebody's got a they may know their prescription is like a minus two. And so to establish a minus two, let's say the front curve of the lens has a, what we'd call, the plus-four curve on the front. We'd have to cut a minus, a concave curve on the back of a minus six so that the math between the two becomes a minus two.
FLATOW: When you say you cut, do you actually use a cutting tool to cut this?
Dr. ENRIGHT: We use a lathe generator, a three-axis generator, lathe, that'll actually cut the back surface of the lens.
And the generators these days are so sophisticated that in the old days, we used to just cut two curves on the back of the lens to establish the prescription. And now at this point, we can actually do such detailed design so that we could actually do a full, what's called a progressive lens and no-line bifocal, to cut multiple curves on the back of a lens now to actually a full, no-line bifocal on the back of a lens.
FLATOW: Talking with Larry Enright at Perferx Optical in Pittsfield, Massachusetts, 1-800-989-8255.
I know, I've had bifocals, and they have that little line in them. How come how do you get these to not have that little line, demarcation line, for the two lenses in there?
Dr. ENRIGHT: That's a good question. I can only answer it to a certain degree. You know, we work with a number of manufacturers, and, you know, we're actually affiliated with a company called Essilor, who has the leading progressive design in the world, actually. And they've got a lot of sophisticated numbers that they come up with to optimize, you know, basically almost erasing that line.
But they do it by actually having a variety of curves in that lens. And so like a bifocal, you can only see in two different distances, distance and near. A progressive lens lets you see clear near, far and everywhere in between. And so there's a lot of really detailed formulas to really, you know, optimize that for the patient.
FLATOW: And where can the mistakes happen because sometimes you send your glasses back and back and forth. Where do some of those mistakes happen in the lens-making process?
Dr. ENRIGHT: Sure. It can happen in a number of areas. You know, we've seen some differences that'll happen. You know, when the patient gets the lenses, are they going through something, some physical changes at some point? Are they under new medication from when they first came in for the exam so that their eyes might be actually acting differently from that end of it?
But, you know, we go through a number of both things at our lab, as well as at your, you know, optometrist, optician's practice that they'll verify these lenses are actually correct.
And so the patient might have some issues with the base curve of the lens, where they might have previously - the previous pair might have had a different curvature on the front of the lens.
And then what's in the past, people used to run into more of an issue of an ABBE value issue, dealing with if they've got a really difficult prescription, you know, we try to put them in a more optimal material. Like, you know, a high-index lens will have a better ABBE value than what another material, like a polycarbonate.
FLATOW: So polycarbonates now make up about what percentage?
Dr. ENRIGHT: I think we're seeing that anywhere from 40 to 45 percent of all of our lenses made are polycarbonate, and that continues to grow.
You know, in the old days, it was really not a good material at all. It was good impact-resistance-wise, but, you know, since the onset of the DVD and CDs, they've had to really improve on that, the polycarbonate resin. And so it's helped the clarity of that product substantially.
So it's a great material, one that we use often. And, you know, so it's able to give you the thinner, lighter lenses, as well as one of the most impact-resistant lenses.
FLATOW: All right. So after you cut the lens to the proper prescription, is it finished?
Dr. ENRIGHT: No. So we'll have a big, round lens, which somebody else referred to it looks like a big contact lens, if you will, at that time. And then we'll take your frame that you chose, and we'll put this on some different equipment that'll, you know, basically cut the lens down.
And everything we use is diamond-impregnated metals or wheels to help cut the lens down. And so then we'll use a piece of machinery to actually trace the inside of your eyeglass frame, and then we'll cut the lens to match that.
We'll assemble it. We'll verify that the prescription's right. And hopefully, your patient got a glare-free lens, which will allow them to have improved vision and durability of their lens product, as well.
FLATOW: Is it clear plastic when you start out with it?
Dr. ENRIGHT: You know, it is. It's something you could actually see through when we first start out with it. But as we run it through our manufacturing process on the first side, after we cut out the generator, we have to run through almost like a little lens spa treatment, where we'll start with more of a, somewhat of a sandpaper effect on the lens with cold water.
And then we use a soft felt type of a pad, along with a polished material that'll help to bring the luster up of the lens so you can actually see through it again.
FLATOW: A lot of people are taking vacations. They're going overseas. They go to China, for example, and they're getting very, much cheaper eyeglasses over there. Is there any downside to that?
Dr. ENRIGHT: Yeah, you know, I kind of hesitate to give you a little teaser on this, but, you know, we've actually done somewhat of a study to look at some of this where, you know, people have gone to some online companies that are out of China.
And we've done some impact-resistant testing on some of the products that have come back, and many, if not all, of them have failed substantially. And, you know, I think we take for granted some of the safety precautions we do in the States here.
And, you know, everyone driving a car nowadays, that has a high-impact airbag, and if you're wearing one of those lenses that are from overseas like that, they've got different standards than we have, from the FDA impact-resistance standards.
And that airbag goes off, chances are that's going to shatter your lenses that you're wearing in that frame. And so that would be unfortunate if somebody saved a couple dollars to then lose vision in their eyes because of that.
FLATOW: Let me get a quick question from Jeff(ph) in Minneapolis. Hi, Jeff.
JEFF (Caller): Yes, hello.
FLATOW: Hi, go ahead.
JEFF: Yes. I'm curious about why it is not possible to fix a scratch or otherwise some damage to a lens. I'm a welder, and I get a lot of sparks or grinding sparks on my lenses sometimes, and it's pretty expensive to keep buying new glasses all the time.
FLATOW: Good question.
Dr. ENRIGHT: Yeah, a lot of welders still use glass lenses because of their overall durability. There's, you know, there's new products out. There's some of these glare-free lenses. They're the most durable products now that are available, even more so than glass.
But in a profession such as welding, you know, we actually have to the tools that we use to surface and take the scratches out of lenses when we actually manufacture the lens are quite large, and we wouldn't once the lens is actually cut down to the frame size, it really wouldn't be possible to, you know, mount it to the tools that we use to take the scratches off of it.
FLATOW: Are there different qualities of plastics? I mean, can you ask for a premium plastic versus a normal lens and get a better type of lens or better vision out of the plastic?
Dr. ENRIGHT: Sure. Yeah, well, one of the big things that everybody should be talking to their eye care professionals about is certainly the new glare-free lenses. You know, if you think about it, you know, you want to get as much light to your eye as possible to be able to have the best vision. And the best way to do that is by asking for a glare-free lens.
And the new products that are out there today allow up to, in some cases, even 11 percent more light into the eye, and so it'll obviously allow you to see better.
You know, think about if you're a dim room, it's harder to see that way unless the lights are brighter. And so and these new glare-free lenses, they're not only - allow you to see better, but cosmetically, it looks better. And then furthermore, they are the most durable and easiest-to-clean lenses on the market right now.
FLATOW: Should you ever feel self-conscious about taking the glasses back if they don't work, they're not working for you?
Dr. ENRIGHT: I think that's another, that's a really good question, actually that you'll see some of these advertisements online. A lot of those independent eye care practitioners out there, their livelihood's based on your happiness. And so they want you to have - they want you to be happy with their final product.
And so absolutely bring those back. Don't hesitate to say, gosh, for whatever reason you're unhappy with them. I'll tell you right now, 99 out of 100 of those optical practices are going to make sure that you're satisfied.
FLATOW: And one last question: How do these transition lenses work, you know, the ones that get darker in the sunlight?
Dr. ENRIGHT: Yeah, those are that's pretty amazing technology. They imbibe the lens with they're transitions material that actually becomes part of the lens itself. And actually, they'll bake it into the lens.
And what happens is these molecules are actually activated by UVA and UVB light. So UVA light's when you go outside. And when those molecules are activated by the light, and depending on how much light hits them, more and more of those molecules will activate.
And it's really an amazing technology to know that it's an intelligent lens now that knows if it's you know, we've got an overcast day in the Berkshires today, that it wouldn't activate very much outside today. But if it was a very bright day, especially in this time of the year, it would get sunglass-dark.
FLATOW: Well, we wish you a good fall and the turning of the leaves up there in the Berkshires.
Dr. ENRIGHT: Thanks so much.
FLATOW: Thank you for joining us. Larry Enright, general manager of Perferx Optical in Pittsfield, Massachusetts.
We're going to take a short break, and when we come back, we're going to talk about a new book: "Yellow Dirt." Stay with us. We'll be right back.
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FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY, from NPR.