Poly or Hi-Index

[UFRich]

Forgetting the optical qualities of the lenses, what is the thinnest lenses available today?

Is Poly or 1.67 thinner?

Does 1.74 make that much difference?

How about 1.60 Hi Index?

UFRICH:cheers:

[Cowboy]

UF,

I have found on Rx's above +/-4.00 that 1.67 proved to be much thinner than poly. I especially like the Seiko 1.67. I have not used a 1.74, but I would suspect that it will probably cut down in only miniscule proportions. My mother is a -11.00 and I put her in a CK drill mount with 1.67. i loved the result over poly (she was in that previously) I knocked of about 1mm or so in the thickness area and provided a medium roll with high luster polish (1.67 shines like no other) and the rx looks like a -6.00. I can't tell you the pleasure it brought to my mother to have such a 'thin' pair of eyeglasses.

That is my opinion and I'm sticking to it!!

Cowboy

[For-Life]

I find poly to be thinner than 1.6 (that is Airwear poly). I find that a 1.67 (Essilors TL 1.67) is thinner than poly, and that a 1.74 is thinner than all of them. Of course this would be comparing appropiate scripts. The thinnest lens available to my knowledge is 1.9 Glass.

[Jedi]

Ditto on the 1.9 glass, but from my understanding in the US it has a thicker minimum C.T. than anywhere else virtually excluding it from the US market, correct me if i'm wrong. I posted in another thread, that I found the thickness of 1.74 vs. 1.67 in anything under a -9.00 was undetectable.

[RT]

I wasn't aware that the 1.74 material was available in the US.

HOYA makes the 1.70 index EYRY material, which is aspheric for single vision and can be ground to a 1.0 mm minimum center thickness (and is drillable). As Cowboy notes, however, using an ultra-high index material won't always get you a thinner lens--there are minimum edge thicknesses required for mounting lenses. A plano in 1.67 or 1.70 won't be thinner than a plano poly, and will weigh more!

For a -10.00 in a 50 eye with no decentration, the 1.70 index will be 0.1 mm thinner than the 1.67, assuming that both are ground to the same center thickness. However, many labs do not grind the 1.67 below a 1.2 mm center thickness, so that would add more thickness to the edge as compared to a material that is ground down to 1.0. Depending upon your lab's standard, I could easily engineer a job where a 1.0 CT poly is indeed thinner than the 1.67 lens.

You'll probably need to quiz your lab a little bit on exactly what lens materials they use and what their minimum center thickness setting is. It is a bad assumption that all labs will produce a 1.60 lens to the same thickness. That's because there is more than one 1.60 material, and they are chemically very different.

For Poly, some labs use a 1.3 mm CT, others have a standard 1.5 mm CT, and will grind to 1.0 for an extra fee. When you talk about 1.60, you're not talking about one material--there are several different 1.60 materials with different minimum thickness standards. Some manufacturers use a "cushion coat" that enhances the impact resistance of the lens, and allows it to be ground thin and still pass FDA tests. Chances are if you just order "1.60", you're getting one with a 1.5 mm CT.

Clearly the minimum center thickness will have an impact on the edge thickness. Check with your lab as to exactly what their high index products are and their specs.

[Robert Martellaro]

In minus powers, Zeiss 1.9 with a .8 to 1.2mm ct. This lens is not tempered, and is available in the US. Talk to "Elka" at Zeiss Corp.



-10.00DS 50mm round blank

................... 1.66.............Poly

Edge...........6.80mm........7.65mm

Weight........7.19gm.........6.41gm

-5.00DS 50mm rd blank

..................1.66............Poly

Edge..........3.75............4.12

Weight.......5.02...........4.38

All 1mm center thickness non-aspheric. Note that poly is still lighter than 1.66 due to poly's lower specific gravity.

1.74, depending on the power, will be about 10% thinner than 1.66. Like 1.66, 1.74 has a high specific gravity (1.47gm/c3), higher than any other non-glass lens.

1.60 is similar to poly except for a higher specific gravity. Exceptions are Sola's Finalite, and one of the 1.60 products from Seiko.

Hope this helps

Robert

[For-Life]

I do get some Americans come into my store, because of the thinner lenses available here (thinner centre thickness and materials). But I will try to use 1.9 glass as a last resort. 1.9 glass is better than 1.8, because they use titanium instead of lead to thin it down, but you are still giving your customer a lot of trouble. There are other avenues. My favourite is to fit glasses on top of contacts. This works great if the customers rx is a -17.00 or higher.