# Optical Forums > Progressive Lens Discussion Forum >  1.74 vs 1.76 double aspheric lenses

## hervens

Hello, new member here
Im currently dealing with the following big prescription: -16 on one eye, and -18 on the other.

What would be the approximate size difference, in terms of thickness of the lens at the edges, between 1.74 double aspheric lenses and 1.76, if any at all?
Are 1.76 lenses worth the extra price investment?
Btw, the chosen frame has a lens diameter of 47mm

Thanks!

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## Jacqui

I don't think you will see much difference if any. This is not from calculations, but from experience.

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## marktheeyeguy

How about some contact lenses first and then glasses on top? Help them out!  LASIK?

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## EyeCare Rich

1.76?  Am I missing something?  Is this a Canadian material.  I have not seen it.  Guess I better get on the research boat now!

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## Jacqui

> 1.76?  Am I missing something?  Is this a Canadian material.  I have not seen it.  Guess I better get on the research boat now!


It's made by Tokai in Japan, not seen much here for some reason.

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## optical24/7

Last I heard it didn't pass our drop ball test required here in the U.S.

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## sharpstick777

> It's made by Tokai in Japan, not seen much here for some reason.


The problem is that coating on 1.76 is not index matched, although they are working on it.  There is an enormous amount of bi-refrigence in the 1.76 samples I have.  They did pass a drop ball test in the lab, though.  I measured a 1.74 and 1.76 in a -12.00 and thickness difference was insignificant.

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## sharpstick777

Generally, a bi-concave lens is thinner over a -14.50, however, the front side cosmetics are strange.  

I would contact Ice-Tech.  We did a 1.74 -24.00 in a 49 eye that finished out with an 8.4 mm edge thickness.  It looked amazing.  They use a patented thinning process, on special modified generators, with software they wrote from scratch, on blanks they make in-house.   




> Hello, new member here
> Im currently dealing with the following big prescription: -16 on one eye, and -18 on the other.
> 
> What would be the approximate size difference, in terms of thickness of the lens at the edges, between 1.74 double aspheric lenses and 1.76, if any at all?
> Are 1.76 lenses worth the extra price investment?
> Btw, the chosen frame has a lens diameter of 47mm
> 
> Thanks!

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## TokaiAU

Hi Guys, I couldn't help but notice this thread. The cataloged edge thickness of the Nikon 1.74 DAS for a -17 with a 60mm blank is 13.9mm and the cataloged edge thickness of the Tokai 1.76GO is 11.4mm also with a 60mm blank. I hope this helps.

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