# Optical Forums > General Optics and Eyecare Discussion Forum >  polycarbonate v. high index lens

## nelce

hey guys, i was just wanting to seek some advice regarding my lens.  i recently put in an order at pearlevision to have my glasses & lens made.  my prescription is OD -8.75, OS -6.25.  i am seeking the thinnest and lightest lens possible, and at pearlevision, they told me their "microthin plus" lens made from premium polycarbonate is their thinnest lens.  however, i'm hearing from many sources that the high index lens is even thinner?  is this true?  when i confronted pearle vision about it, they told me they use "polycarbonate plus" which is thinner than high index, and that high index is only thinner than ORDINARY polycarbonate.  

here is pearle vision's website on the microthin plus lens: http://www.pearlevision.com/webapp/w...&storeId=10001

any insight on which is thinner for my prescription?  these "microthin plus" lens made from premium polycarbonate or the high index lens.  thank you all in advance!

----------


## HarryChiling

They are refering to aspheric polycarbonate lenses, but  you can get high index lenses in a aspheric design as well.  The high index in an aspheric design is going to be thinner than a polycarbonate.

----------


## RT

Harry, you're only half right.  If you're comparing an aspheric Poly with a 1.0 mm CT to a higher index (1.60, 1.67) that is only surfaced to a 1.5 mm CT, and the frame isn't huge, the poly will be thinner.  Note that in the US, most 1.60 and 1.67 products require either a minimum CT of 1.5 - 1.8 to pass the impact resistance standards, or a "cushion coat" to enhance the impact resistance at lower thicknesses.

It is fairly easy to engineer real world situations where higher index does NOT equal thinner.

----------


## OPTIDONN

If you took an aspheric poly lens with a 1.00 CT and an aspheric 1.66 to a 1.70 high index with a 1.5 to 1.8 CT I feel pretty confident that the high index lenses will be thinner than the poly.

----------


## OPTIDONN

Also keep in mind that the higher the index the less curvature is needed. This will result in a thinner profile. Going by CT is not the most accurate way to judge a lenses overall thickness.

----------


## Robert Martellaro

Due to index of refraction alone, 1.66 is 12% thinner than 1.586 (poly). 1.66/1.67 is available with a 1mm center thickness (finished).

----------


## nelce

thank you all for your replies :)

so i called up costco..i was thinking about transferring my frames to fit the lenses there...they sell a 1.67 high index lens.  will this be a thinner lens for my high prescription compared to this aspheric polycarbonate lens that pearle vision is offering me?  i don't really have any information on the CT though...

----------


## Happylady

> thank you all for your replies :)
> 
> so i called up costco..i was thinking about transferring my frames to fit the lenses there...they sell a 1.67 high index lens. will this be a thinner lens for my high prescription compared to this aspheric polycarbonate lens that pearle vision is offering me? i don't really have any information on the CT though...


The thinnest lens you can get in the States is a 1.74 high index. Generally speaking the higher the number the thinner the lens. With your prescription the 167 should be fine, though.

----------


## OPTIDONN

> thank you all for your replies :)
> 
> so i called up costco..i was thinking about transferring my frames to fit the lenses there...they sell a 1.67 high index lens. will this be a thinner lens for my high prescription compared to this aspheric polycarbonate lens that pearle vision is offering me? i don't really have any information on the CT though...


Keep in mind that the change in thickness MAY not be extreme. Depending in the amount of asphericity etc. etc. that vary from one manufacturer to another it could be as little as .5mm to 1.5mm.

----------


## AWTECH

Unfortunately the question you are asking can not be properly answered here since there are so many variables.

My company produces lens from 1.67 MR-10 using freeform surfacing technology and are custom made aspheric design rather than a premade aspheric design and the way we process a 1.67 lens will result in a thinner lens than the traditional 1.67 aspheric processing.  We place the aspheric design on the back surface and this will result in a thinner individualized.  Using traditional methods for making the lens you could get two different thicknesses from two different labs based on each labs production standards.

The type of retail opticals you mention will offer you good basic quality lenses, however for specialized products, few of these type of retailers offer specialized products such as the lenses that my company makes.  Different labs have different center thickness minimums.  

With your strong prescription you may want to consider a truely custom lens that is individualized.  These will cost considerably more than a traditional aspheric design, so it depends on how much you are willing to pay for the thinnest lens possible.

----------


## mirage2k2

what about optical quality?  I made the mistake of going for the thinnest lightest thing that money could buy and ended up with lenses that gave me eyestrain because the vision was not good enough ... the fact that they cost SO MUCH just rubbed salt into the wounds  :Mad:  My advice, for what its worth, get the thinnest lense that also provides good optics ... with rx OD -8.75, OS -6.25 I would not touch polycarbonate or 1.74 ... go for a good 1.6 ... Hoya eyas, Sola finalite ... the ones with ABBE above 40.

----------


## OPTIDONN

Chromatic aberration can be annoying but in general will not riun the optical quality of the lens. I would be more concerned about marginal astigmatism created by a well meaning optician by selecting a base cure thats too flat in order to make the lens thinner. Besides if the eye is well centered and the frame small enough the chromatic aberration will be minimal.

----------


## AWTECH

Mirage2K2:  Unfortunately many people blame Abbe Value for their adaptation problems, when in fact there is no equipment at the optical retail level to prove or disprove this.

For example I would estimate that more than 99% of the Rx jobs filled in both 1.60 and polycarbonate if surfaced in the same manner to the same standards would provide comparable vision.  Abbe value is not the problem in over 99% of the cases even though it is pointed to as the problem.

I would be curious to know in your cited example how you concluded your vision problem was related to Abbe Value.

----------


## OPTIDONN

> Mirage2K2: Unfortunately many people blame Abbe Value for their adaptation problems, when in fact there is no equipment at the optical retail level to prove or disprove this.
> 
> For example I would estimate that more than 99% of the Rx jobs filled in both 1.60 and polycarbonate if surfaced in the same manner to the same standards would provide comparable vision. Abbe value is not the problem in over 99% of the cases even though it is pointed to as the problem.
> 
> I would be curious to know in your cited example how you concluded your vision problem was related to Abbe Value.


You have a good point. Chromatic Aberration is probably one of the better known aberrations by both eye care professional and consumer alike. As a result I think it get blamed for alot of things that are totally unrelated.

----------


## Diane

MR-10 with index of 1.67 has superior optics, super thin, better tensile strenght, superior solvent resistence, more resistant to temperature extremes....better than poly.

You'll pay more for it than poly, but it is a better product.

Just my 2 cents worth.

Diane

----------


## For-Life

Here is the thing, what is the rx?  What is the PD?  What is the frame size?  Ect.

Even add to that the centre thickness and such.  Are we really helping this consumer thus far?  Probably not.  Lets get our answers to be answered by the fitters, and maybe give the poster some guidance.

----------


## mirage2k2

> I would be curious to know in your cited example how you concluded your vision problem was related to Abbe Value.


 ... sorry guys forgot to mention my 5d base out prism ... which does give me considerable trouble with my +6 rx in 1.74 lenses.  The sharpness of the vision is definately affected by the amount of prism ... and although my optician has not been able to measure the amount of chromatic aberration, as AWTECH has suggested, they have made several lenses with differing amounts of prism and the ones with lots have poorer vision than the ones with less ... for example, with a 4d left the chromatic aberration (mainly color seperation) is clearly visible when I look straight on ... I dont even have to look off-axis to see it  :Eek:  ... thanks to the OC already being displaced by several mm.

In this thread I saw the rx of -8 or so and thought ... off-axis vision ... lots of induced prism + low abbe = lots of chromatic aberration.

----------


## AWTECH

Mirage 2K2:

You could be seeing different colors as you describe due to hard coating.  I assume you have hard coating and anti-reflective treatment.  I doubt that the lenses are processed with a hard coating with an index of refraction greater than 1.60 and it may only be 1.50.  This hard coating differencial could be why you are seeing different colors in certain viewing angles.

A lower index lens material with matched hard coating may stop the problem.  You could find that a hard coating of 1.60 on Poly could eleminate this issue even though you would have an abbe value that is not that high.

Conclusions about abbe value that many people draw is like conclulding that if you drive down the road you are going to die.  You can make this conclusion about dying if you use the following premise. When I drive down the road I may cross the center line at the same time a large bus is approching at high speed. Based on these facts you are likely to die driving down the road, however the number of people who cross the center line at the exact time a bus is fast approching is a very small percentage of people driving.

My above example is to point out that there are many factors that can cause one to draw an incorrect conclusion and without the method to test your premise that the abbe vaue of the lens is the problem, there is no basis to conclude that tht problem with your vision is caused by abbe value.

As OptiDonn stated:


> Chromatic Aberration is probably one of the better known aberrations by both eye care professionals and consumers alike. As a result I think it gets blamed for alot of things that are totally unrelated.


The original question of this thread?  The tinnest lens possible is going to cost considerablly more than the lens that was recommended.  Thsi recommendation could have been made due to the patient statements during the fitting that he wanted a total cost within a certain range.  Let a competent eyecare professional guide you with your total selection and do not think that you can become an expert by seaching the internet and asking a question and getting a total answer on line.  Without seeing the patient and the total sum of the information at the same time a proper recommendation can not be made.  The answer to your question is quite different if cost is not object, vs. you have a specific budget range.

----------


## OPTIDONN

> MR-10 with index of 1.67 has superior optics, super thin, better tensile strenght, superior solvent resistence, more resistant to temperature extremes....better than poly.
> 
> You'll pay more for it than poly, but it is a better product.
> 
> Just my 2 cents worth.
> 
> Diane


Superior optics? OK I use this phrase all the time with out thinking about it. Aside from abbe how would these other materials have better optics? And how much does abbe affect the optical performance of the lens? Design and physical properties may be better but these are seperate from the optical properties. I think I should stop using that phrase and come up with something else.

----------


## OPTIDONN

> ... sorry guys forgot to mention my 5d base out prism ... which does give me considerable trouble with my +6 rx in 1.74 lenses. The sharpness of the vision is definately affected by the amount of prism ... and although my optician has not been able to measure the amount of chromatic aberration, as AWTECH has suggested, they have made several lenses with differing amounts of prism and the ones with lots have poorer vision than the ones with less ... for example, with a 4d left the chromatic aberration (mainly color seperation) is clearly visible when I look straight on ... I dont even have to look off-axis to see it  ... thanks to the OC already being displaced by several mm.
> 
> In this thread I saw the rx of -8 or so and thought ... off-axis vision ... lots of induced prism + low abbe = lots of chromatic aberration.


OK 5 diopters base out with a +6.00 rx that can make you crazy! My rx is around a -4.00. When I worked at Lenscrafters I had a pair of safety glasses made in poly. I chose an aviator shape, don't asky why!. The excessive thisckness created significant chromatic aberration. It really did not affect the optics of the lens but I found it very, very distracting.

----------


## nelce

hey guys. i just got my glasses from pearle vision, and on the receipt mentioning what was done to the lens, there's a number under the "cylindrical" and "axis"?  I thought these values were astigmatism, which I don't have...could these values mean anything else?

----------


## OPTIDONN

> hey guys. i just got my glasses from pearle vision, and on the receipt mentioning what was done to the lens, there's a number under the "cylindrical" and "axis"? I thought these values were astigmatism, which I don't have...could these values mean anything else?


Nope! they are for astigmatism.

----------


## nelce

thanks for your reply.  damn it, pearle vision just keeps screwing up.  and i wore those glasses for an hour or so...feeling weird....i hope they didn't make my vision worse :(

----------


## loncoa

It's the optometrist who would have prescribed the cylinder in your prescription. I expect that you DO have astigmatism, but if you doubt it, or if you wear the glasses for a week straight and they don't start to feel fine, you need to contact the optometrist.

----------


## nelce

> It's the optometrist who would have prescribed the cylinder in your prescription. I expect that you DO have astigmatism, but if you doubt it, or if you wear the glasses for a week straight and they don't start to feel fine, you need to contact the optometrist.


um.  actually i don't.  and my prescription ALSO says that i don't. pearle vision is the one who ADDED the prescription for astigmatism in my lens.

----------


## Happylady

> um. actually i don't. and my prescription ALSO says that i don't. pearle vision is the one who ADDED the prescription for astigmatism in my lens.


That doesn't make sense. Do you have a copy of your prescription? Why would Pearl add in an astigmatism correction?

----------


## nelce

> That doesn't make sense. Do you have a copy of your prescription? Why would Pearl add in an astigmatism correction?


yep, i do have a copy of my prescription.  and the only thing on it are two numbers: OD & OS.  i'm thinking they screwed up...

----------


## Happylady

> yep, i do have a copy of my prescription. and the only thing on it are two numbers: OD & OS. i'm thinking they screwed up...


If they really put cylinder in your glasses and its not supposed to be there then take them back right away. Make sure you take a copy of your rx with you.

----------


## Chris Ryser

> *My advice, for what its worth, get the thinnest lense that also provides good optics ... with rx OD -8.75, OS -6.25*


Sadly enough that does not exist.................................

When you go back in the history of lens curves and their visual performance you can see that lenses progressed from:

*Bi-convex or bi-concave, which made the thinnest and flatest lenses.............*

*Plano convex or concave which was the next step in visual quality............*

*Meniscus lenses, which were based on base curve of + or - 6.00*

*Corrected curve lenses, which provided the best visual effects with the least or none of distortion and aberration off center and towards the edges*.
By going to high index lenses you are compromising the visual quality in favour of the thin cosmetic effect of the lenses. 

Polycarbonate lenses are also high index lenses and higher the index the flatter the lens curves and the worse the optical quality. 

*With the newer high index materials you are actually regressing to historic times in quality of vision for a much higher price, but you will have the cosmetic benefit.*

----------


## mirage2k2

> *With the newer high index materials you are actually regressing to historic times in quality of vision for a much higher price, but you will have the cosmetic benefit.*


:D :D :D

----------


## mirage2k2

> ... higher the index the flatter the lens curves and the worse the optical quality.


Doesn't asphericity fix all of the visual errors introduced by the flatter lens form? :D

----------


## francisOD

Although I agree with most everything that has been said on this thread, I find it odd that none of you have mentionned the 2.50 anisometropia...I would recommend having equal base curves to minimize image size difference...some patient are that sensitive.  Also a smaller frame will minimize the Prentice rule effect and dimish his chances of seeing double in the periphery of the lens.  Just an OD's perpective...

----------


## OPTIDONN

> Although I agree with most everything that has been said on this thread, I find it odd that none of you have mentionned the 2.50 anisometropia...I would recommend having equal base curves to minimize image size difference...some patient are that sensitive. Also a smaller frame will minimize the Prentice rule effect and dimish his chances of seeing double in the periphery of the lens. Just an OD's perpective...


I'm sure an iseikonic lens would help but this raises a question that I'm not to sure about. I know that slab off must be prescribed but what about using iseikonic lenses? Is this within the realm of an optician?

----------


## francisOD

By iseikonic lenses, if you mean choosing a proper BC for the prescription, I believe it is.  As an OD, if a patient asks for his prescription, it never includes BC.  Most of the time the labs determine the best BC.  In a situation like this, I think it is very reasonable to ask for matching BC.  Some labs would do this without you asking for it but as the optician, you are the one that can recommend what is best for the patient to make sure it does not fall through the cracks at you lab.  If you specified matching BC, then you protected yourself and your patient.  Just my opinion though!

----------


## Robert Martellaro

Francis,

I'm looking at the shape factor formula for spectacle magnification and I believe we would want to increase the base curve on the left lens instead of decreasing the curve to match the right lens. My feelings are that if there are no symptoms it's usually best to leave well enough alone, considering the appearance and poor off-axis optics of lenses optimized for image size.

Optidonn,

Single vision wearers usually posture and hold objects higher, decreasing the reading depth, minimizing the vertical imbalance. However, multifocal wearers who perform frequent and/or prolonged close tasks would certainly benefit from a slabbed lens. 

Regards,

----------


## OPTIDONN

> By iseikonic lenses, if you mean choosing a proper BC for the prescription, I believe it is. As an OD, if a patient asks for his prescription, it never includes BC. Most of the time the labs determine the best BC. In a situation like this, I think it is very reasonable to ask for matching BC. Some labs would do this without you asking for it but as the optician, you are the one that can recommend what is best for the patient to make sure it does not fall through the cracks at you lab. If you specified matching BC, then you protected yourself and your patient. Just my opinion though!


A specific base curve should be chosen based on how it will effect aberrations not image size. If you begin to change the lenses parameters ie, thickness, base curve, vertex distance, all with the intent of changing retinal image size then you have an iseikonic lens. I can see if an optician changes a few things here and there to increase patient adaptability but is making a full blown iseikonic lens within the real of an optician? Or should it be prescribed?

----------


## francisOD

OptiDon,

From what I remember about this portion of optics, over 80% of image size is related to BC.  If both BC are equal, you will minimize image size disparity.  The BC selection in a case like this I am not sure on.  I would talk to my guy at my surfacing lab and get feedback from him before deciding.  :cheers:

----------


## francisOD

Robert, I agree with you...I was just wondering if anyone had taken this into consideration.  If there is no symptomatology in a case like this then there is no cure needed.  However if patient has adaptation issues, increased headaches or other vague complaints, this would need to be considered as a source of those complaints.  Cheers!!

----------


## OPTIDONN

> OptiDon,
> 
> From what I remember about this portion of optics, over 80% of image size is related to BC. If both BC are equal, you will minimize image size disparity. The BC selection in a case like this I am not sure on. I would talk to my guy at my surfacing lab and get feedback from him before deciding. :cheers:


OK! My mind is some where else right now:hammer: 

I was assuming that you were basing correct base curve selection on image size and not the corrected curve theory to minimize lens aberrations. But in a case like this if you were to regulate image size one of the first places to start would be base curve! Duh! This is what happens when crazy kids keep you up all night! You start reading things that aren't even there!:(

----------


## francisOD

Optidon, I have a 2 and 4 year old (2 girls)...I now how it feels.  No damage done.  Happy to see you agree.  Cheers!!

----------


## OPTIDONN

I've got a two year old and a 9mo. old both girls too! I think its rough now I'll be in a straight jacket when they are teens:hammer:

----------


## francisOD

I'll I can say Optidon is may the force be with both of us...:cheers:

----------


## sharpstick777

Old Dead Thread of the Week::  Since it seems on here that a terribly old thread gets dug up every 2 weeks or so, and a mess of people comment on it before they realize the folly...

Admins, many forum software and groups will auto-lock a thread if its over a certain time without a reply.   I don't know if that is possible with the software Optiboard uses, but it would held promote new discussions, and shorter threads that don't exist over the course of decades.  It should be based on last comment, not when it was started.   It would still be visible.  

Some discussions simply need to die.  What say ye?

----------


## pseudonym

Consumer thread, consider it dead.

----------


## becc971

You should be going to a reliable doctor's office with a good optician and asking them these questions and probably ordering from them too.  Costco? pearle? really?  just my two cents.  chains give too much pressure to employees to make that cash money.

----------


## m0002a

> Old Dead Thread of the Week::  Since it seems on here that a terribly old thread gets dug up every 2 weeks or so, and a mess of people comment on it before they realize the folly...


This thread *was* dead for 8 years until you revived it, and now see what happened when you did that !!!

----------

