1.67 vs 1.74?

I just edged two stock -8.00 sph lenses to make a display. Here are the specifics:
A=48, PD=30.0 OU
Right: 1.67 Somo, BC=0.0, CT= 1.1mm, Max Edge Thickness=5.1mm
Left: 1.74 Nikon 5, BC=0.25, CT=1.1mm, Max Edge Thickness=4.9mm

The difference in edge thickness at 0.2mm is barely perceptible. This is not what I had hoped for. The Opticampus calculator predicted that the 1.74 would be 0.5mm thinner on the edge, even when the difference in BC was entered. At 1.1, Both CTs were less than I had anticipated.

Why is the Nikon 1.74 made on a 0.25 BC, instead of 0.00?
Why are both center thickness at 1.1 when I can't find a lab to grind one to less than 1.5?
Why only a 0.2mm difference in edge thickness, when the calculator predicts 0.5mm?
Why would a consumer pay the hefty premium for 1.74?
Is the Nikon 1.74's AR Crizal Alize? It IS slick as snot.
What is your experience with 1.74 lenses?

MarcE said:

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Why would a consumer pay the hefty premium for 1.74?

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Your example is great for pointing out the problem of selling products that are not properly represented to you by the manufacturer.

How would the consumer benefit from one of these lenses to another?

Does the patient really care if it is a SOMO or a Nikon?

Different aspheric designs is one issue. One is optimized for a base curve of 0.25 while the other is optimized for 0.00 base curve.

Thickness is not the total answer the total look of the lens in the frame is also very important and possible in many cases more front curve and a little more thickness will yield a better looking job. With the correct lens design using individualized lenses and a backside aspheric design and a front spherical curve you can a great looking lens.

I guarantee you if you decentered more OR if you choose a larger frame, you'd see the difference more clearly. I wear about a -6, and I recently made myself a pair of 1.74 with Alize lenses. Previously I had worn 1.67. The new pair are thinner by almost a mm than the old pair, and -get this- the new pair is WIDER (bigger eye size and more decentration) than the old pair. As you move away from the OC, the difference becomes more and more visible!
Here's a small word of warning for you though: If you're getting the same 1.74 lenses I am (I'm not sure if they're Nikon but I got mine thru essilor's lab) they are ground in Puerto Rico or something and take forever to come back. They take up to two weeks to make it through customs and I've ordered a couple pairs that I had to keep sending back. Three remakes at 3 weeks a piece...not a happy customer even if they were thin as a credit card.

From reading these boards I got the impression that the 1.74 is useful when the rx is about a -10.00 or greater. Below that the difference isn't that much.

However, my -6.00 daughter recently got a pair of semi rimless glasses and wanted the thinnest possible. She got the 1.74 and is happy with the results. I told her the 1.67 would be about the same but it would be interesting to see both made up. Her PD is very narrow, about 57.

Happylady-
Did it make a difference in thickness? Mine are definately thinner than the 1.67s I had before (see my post above).
The other thing I noticed is much less distortion in the edges. I can literally look through the corner of my lens and see as well as through the center! I just love them. Mine are in drill mts. also, which is great when a patient tells me their Rx is "too strong" to wear that frame and I tell them my Rx is the same or sometimes stronger!
I did a pair of 1.74s in a -10.50 recently also. They looked fantastic.

These -8.00 lenses are stock. It took about 2 days to get them. Yet another reason that you should buy stock lenses whenever possible for all myope SV and mild hyperope. Also, suprisingly, the CT was 1.1mm on both the 1.67 and 1.74.
The stock range for Nikon 5 1.74 lenses is -3.00 to -10.00; cyls to -2.00. -10.25 to -12.00, spheres only. They run about 60% less expensive than a surfaced lens.

EyeFIT: I would be interested to know what the CT is of your surfaced lenses. My labs won't go less than 1.5mm

Someone tell me if I am wrong:
1. The 1.74 lens wasn't significantly thinner because it was made on a 0.25 BC instead of 0.00, like the 1.67. At a 0.00 BC the 1.67 lens has sacrificed some optically quality to make a thinner lens.
2. I probably shouldn't recommend a 1.74 lens material unless the Rx is over a -9.00. I don't know what the hyperope range should be,yet

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Originally Posted by EyeFitWell

Happylady-
Did it make a difference in thickness? Mine are definately thinner than the 1.67s I had before (see my post above).
The other thing I noticed is much less distortion in the edges. I can literally look through the corner of my lens and see as well as through the center! I just love them. Mine are in drill mts. also, which is great when a patient tells me their Rx is "too strong" to wear that frame and I tell them my Rx is the same or sometimes stronger!
I did a pair of 1.74s in a -10.50 recently also. They looked fantastic.

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It was a new frame so I don't know how thin they would have been in 1.67. Her other glasses have 1.67, but they are in a plastic frame and the edge doesn't show at all. She also noticed how sharp and clear her vision is.

The 1.74 lenses
CT=1.1
ET=3.0
Eye size is 48, shape is cat eye. BC=0.25

1.67 lenses
CT=1.0
ET=3.9
Eye size is 46, rounded
I don't know the BC, but it was a Pentax brand stock 1.67 aspheric lens...very flat.