CR-39 vs. Polycarbonate

[Michael22]

Hello all, I've had this question in the back of my mind for years bothering me and just discovered this board where I can ask other opticians what they think so theres many more to follow. The question I have now are what are the specific downsides of CR-39 over polycarbonate? Other than impact resistance, lens thickness(?), and price, it doesn't seem like the value of poly for some patients is worth it. At this new office I'm working at we have a doc that strictly will not let their patients be put in a polycarbonate lens. I can see the value of it, and how it's such an easy sell, but I guess my big question would be is how much worse is CR-39 *actually* compared to poly? I started off working in the optical industry at visionworks where we were told to push, push, push, but now it seems like their are several instances where polycarbonate is actually a detriment, and not a direct upgrade like i've been saying for years now. If the patient has a low Rx, doesn't care about impact resistance (i.e they are computer glasses that are only at the computer) is it actually a disservice to put that patient in a polycarbonate lens? I feel like I should know the specifics being three years in, but i've just been told so many different things by so many different offices. What would you say on the topic? What about HI 1.67 for patients where poly would be fine, but they get more clarity? How bad are the chromatic aberration actually such that patients would really notice?

Also just kind of a general discussion on materials. I feel like everything I know has been flipped upside down like Will Smith in the Fresh Prince of Bel-Air.

[wmcdonald]

It is different! The Abbe value is significantly higher in CR-39. It can be easily tinted, etc. But the value in poly is simple, it is more impact resistant. This is basic stuff!

[drk]

Always go poly when you can. We use it for almost everything. Thinner, lighter, UV protection, good for semi-rimless, kids, safety, etc. It's inexpensive.

Your doctor is wrong; it's the best value in optical. Most doctors don't know optics at all.

The optics are worse than CR39 but it's power dependent. Low power in poly is the same optics as low power in CR39.

Also, the optics in 1.67 are virtually the same with polycarbonate. Only use 1.67 when the lens power dictates (usually high minus like -8.00 and up).

[drk]

Having said that, though, polycarb is more reflect-y so AR coating is more necessary with it than with CR39.

[Elvis Is Alive]

We do 90% or higher in trivex. Better optics than poly, lighter than both, high impact resistance, in between CR39 and poly in thickness. Slightly higher costs than both.

We are "open access" (not in network) for all vision plans so we aren't concerned with varying insurance co-pays of different materials.

[Michael22]

It is different! The Abbe value is significantly higher in CR-39. It can be easily tinted, etc. But the value in poly is simple, it is more impact resistant. This is basic stuff!

I know that it is basic, but I guess I was wanting to get in depth about exactly how much one would even know the difference with having a lens with a higher abbe value? I've only worn poly my entire life and have never noticed anything out of the ordinary. If I ordered cr-39 lenses would i actually be able to tell the difference? I know poly is impact resistant but how often are people actually dealing with impacts? For children and people who wear them all day/drive in them i can see the value, but how much better is poly over cr-39?

[Michael22]

Always go poly when you can. We use it for almost everything.

What a great reply! I figured the abbe value being lower in poly made it slightly worse visually than cr-39 but the difference has to be so miniscule especially considering everybody usually wants to buy the non-glare coating anyway. You start out high index at -8 and up? I was always told -5 and up or if they have a pretty high cyl like in the 3s. At -7.00+ that's when i start suggesting high index 1.74. Is there anything wrong with that? I've always just done it, asked the optician in charge if it's a good idea, and then just went with it with no issues, but now IM the optician in charge and so these very specific things i feel like i need to know, and there's not a lot of resources on these very specific questions. Thank you!

[Michael22]

We do 90% or higher in trivex. Better optics than poly, lighter than both, high impact resistance, in between CR39 and poly in thickness. Slightly higher costs than both.

We are "open access" (not in network) for all vision plans so we aren't concerned with varying insurance co-pays of different materials.

Yeah we also try to do Trivex for everybody, but sometimes you get those people who just want basic computer glasses they might want to wear an hour a day at night, and it's harder to sell them on the more premium stuff. I always heard trivex is king of materials.

[Kwill212]

Poly is not an upgrade from cr39.

CR39 is chemically inert. Poly will be junked if exposed to chemicals(alcohol, acetone, etc.), it doesn't tint well, optics are worse, CR39 will have much better long term AR performance over poly. Poly always has problems with AR coatings. Anytime someone brings me an old lens with peeling coatings, it is always poly. CR39 is a great material. Trivex is wonderful. Those 2 will cover 75% of your jobs if not more. 1.60 for the rest. and occasionally 1.67. Poly should be stricken from the optical record.

[Michael22]

Poly is not an upgrade from cr39.

Is there any case where you would actually prefer to use it then? Like as impact resistance for kids if they can't afford or don't want to do trivex? Isn't poly more scratch resistant than CR-39?

[drk]

C'mon people.

Polycarbonate's optics are great except for extreme powers. You can't just read an Abbe number off a piece of paper without context. The comparison in optics is NOT CR39 VS. POLY (because at lower powers they're the same) but POLY vs. 1.67 at higher powers. And they're virtually the same. Polycarb does fine with alcohol. Nobody should put acetone on any lens, ever. And it's a big fat lie that poly has trouble with AR. It's just not true.

There's very little usefulness for 1.6. It's a me-too product.

Trivex is a mid-index and great, but just like the argument above for poly vs. CR39, there's no difference in optics in lower powers, and in higher powers, you have great optics but thicker lenses. So it's only unique in it's work-ability.

I hate to say it, but if you don't like polycarbonate you don't know what you're talking about. You're just a hater and you're not experienced or scientific.

[Kwill212]

Is there any case where you would actually prefer to use it then?

No. I think I've done 2 poly jobs this year.

Like as impact resistance for kids if they can't afford or don't want to do trivex? Isn't poly more scratch resistant than CR-39?

In my experience, cost is almost nothing between trivex and poly.

What do you mean "don't want to do trivex"?

Poly is NOT more scratch resistant than CR39.

[wmcdonald]

Polycarbonate lenses are typically material of choice for children, sports, and safety. It is about impact resistance. Does it scratch easier? Yes. It is lower cost compared to Trivex.

[drk]

Does it really scratch more easily than trivex, even with a factory coat? I don't believe so. Plus if there's AR on it...

[Lensman11]

DRK
your logic is incorrect poly is a softer material and because of that the scratch coating does not function as well as it does on a harder material. The same is true for AR coating it is least scratch resistant on Poly.

[Uilleann]

C'mon people.

Polycarbonate's optics are great except for extreme powers. You can't just read an Abbe number off a piece of paper without context. The comparison in optics is NOT CR39 VS. POLY (because at lower powers they're the same) but POLY vs. 1.67 at higher powers. And they're virtually the same. Polycarb does fine with alcohol. Nobody should put acetone on any lens, ever. And it's a big fat lie that poly has trouble with AR. It's just not true.

There's very little usefulness for 1.6. It's a me-too product.

Trivex is a mid-index and great, but just like the argument above for poly vs. CR39, there's no difference in optics in lower powers, and in higher powers, you have great optics but thicker lenses. So it's only unique in it's work-ability.

I hate to say it, but if you don't like polycarbonate you don't know what you're talking about. You're just a hater and you're not experienced or scientific.

If you read nothing else on OB the rest of the year read this.
Well said Doc!

[ChrisBowers]

Kind of a baited question. There are dozens of ophthalmic materials out there all having different properties, purpose, and functions. All these lenses are affected by the type of hard coats factory and lab and or AR stack. There is not one lens that fits all. As for scratch resistance, a 2-minute tutorial on how to clean a lens is the very best time/money spent. Get some books on Ophthalmic dispensing as there is a whole lot that goes into making a great pair of glasses.
Chris

[dima]

Does it really scratch more easily than trivex, even with a factory coat? I don't believe so. Plus if there's AR on it...

Yes poly is less scratch resistant even if coated with the best dip coat, also AR is less resistant (because less bonding in the process... cr39 adheres better)


poly (even the high quality poly) is pretty a crap

We have many materials better for optical quality, scratch and AR resistant, rimless mount:
trivex, mr8, mr8plus, hivex ecc.


Polycarbonate have only 2 points: it is a cheaper material, have an excellent impact resistant even if AR Coated!


Trivex have a similar impact resistance but if AR coat lose part of it


This is why safty glass for industry are in poly

[drk]

I don't even mention safety because to me it's a red herring. The last thing I've seen in my 35 years is an eye injury from a lens of any kind.

I don't know about you, but I don't get coating failures on polycarbonate lenses, ever. At least, not enough to make a difference.

Plus, how long are you expecting these lenses to last, anyway? Five years? If you're looking to make some classic Rx sunglasses that last for a decade, OK, we can talk, but most people (and especially with VCPs and the quality of frames, anymore, and with the downmarkety-turn-and-turn-and-turn el cheapo glasses so you have a blue pair and a purple pair) a pair of glasses is going to last 3 yrs, max.

I think the trick is not to build the ultimate glasses that last forever, but to make a nice 2-3 year pair and get a new pair. That seems to be the trend.

Keep the cost to get into glasses low. This applies to:
1. new wearers' first pairs, because they're not bought into the whole "I really DO need glasses" mentality, yet.
2. kids because they grow so quickly and progress
3. old folks = cataracts and penury
4. any presbyope that wants computer glasses and SVNO designs. They like multiples.

The people that truly appreciate quality glasses are
1. Ametropes since a young age. They know glasses, by now. They know the impact on their lives.
2. High ametropes.
3. Advanced presbyopes. Multifocal designs are critical.
4. I would say Rx sunglass wearers, because they're a "positive" purchase instead of a "negative" purchase. ("You only sell two things: good feelings (sunglasses) and solutions to problems (dress Rx)". Good feelings trump problem-solving every time.)

[Kwill212]

C'mon people.


There's very little usefulness for 1.6. It's a me-too product.

That really says it all. You think one of the best(if not THE best) ophthalmic material made is a "me-too" product. Stick to spinning dials doc.

[drk]

IF YOU BELIEVE (and you apparently do) that poly is crap, 1.6 is your alternative to polycarbonate, then, for moderately high lens powers. Ergo your affinity for it.

IF YOU BELIEVE (as I do) that poly is good, then 1.6 has a very small advantage for a moderately higher price.

I know as much about optics as you do, and probably more, so don't test me. You can have your opinion, but don't arrogate yourself above me on optics and vision. I'm pretty smart and pretty educated and pretty experienced and I have lots of framed things hanging on my walls. Remember: you played that card, first.

[Elvis Is Alive]

We package price Trivex with AR for all SV and Progressives. If someone wants CR39, poly, or mid-index up to 1.60, we switch it at no additional cost. We only upcharge for 1.67 or higher indexes.

Patient doesn't want AR? No problem, we will order lenses without it... for the same cost.

Anyone ever played with an uncoated poly lens? Scratches instantly with nearly anything touching the lens. Poly is fine for patients who are changing lenses frequently thru insurance or otherwise but it certainly doesn't hold up as well long term to harder materials as stated above.

[Kwill212]

We package price Trivex with AR for all SV and Progressives. If someone wants CR39, poly, or mid-index up to 1.60, we switch it at no additional cost. We only upcharge for 1.67 or higher indexes.

Patient doesn't want AR? No problem, we will order lenses without it... for the same cost.

Anyone ever played with an uncoated poly lens? Scratches instantly with nearly anything touching the lens. Poly is fine for patients who are changing lenses frequently thru insurance or otherwise but it certainly doesn't hold up as well long term to harder materials as stated above.

This is exactly what I do. They pay my set lens fee and I determine the best product for the application.

[Kwill212]

IF YOU BELIEVE (and you apparently do) that poly is crap, 1.6 is your alternative to polycarbonate, then, for moderately high lens powers. Ergo your affinity for it.

IF YOU BELIEVE (as I do) that poly is good, then 1.6 has a very small advantage for a moderately higher price.

I know as much about optics as you do, and probably more, so don't test me. You can have your opinion, but don't arrogate yourself above me on optics and vision. I'm pretty smart and pretty educated and pretty experienced and I have lots of framed things hanging on my walls. Remember: you played that card, first.

lol, So touchy doc. How ominous. Remember: I've read your previous posts, on optiboard. **cue menacing music**

[Elvis Is Alive]

Speaking of lens materials, whatever happened to Tribrid by PPG? Trivex quality but in a thinner 1.60 index.

Cherry doesn't carry sell them anymore. Rep told me the company that made it (not PPG i assume) went out of business.