1.67 vs. 1.74 ? WTF ?

[skirk1975]

Ok. Here goes. I used a Shamir Autograph II SV 1.74 for a high RX customer. She had previously worn 1.67. Now, she got the glasses and notices that her periphery is noticably better but, her central gaze seems worse and somewhat blurred? Lenses seem fine? I asked around and got an answer of, "1.74 is just not a clear material. 1.67 is just much clearer"? What is this all about? And I am not talking about abbe value here so don't bring that up. Light dispersion would be more of a peripheral issue anyway, not central. OC height was taken and used. What is up with 1.74? I have used many many Nikon/Essilor 1.74 with AR before and had no problems? Any thoughts anyone ? HELP! :angry:

[gunner05]

Same prog type? What type of Rx? Much change?

[skirk1975]

Single Vision. Not much change at all.

[gunner05]

SV to prog? Dude, that may be your problem in and of itself. Auto II is a great lens, but it's not a SV. What type of Rx power are we looking at here?

[skirk1975]

What are you talking about? It has always been Single Vision. Never wore a progressive. You can certainly get an Autograph II in SINGLE VISION. It is still front and backside digitally surfaced using eyepoint technology. Down to 1/100th of a diopter of accuracy.

[Chris Ryser]

It is still front and backside digitally surfaced using eyepoint technology. Down to 1/100th of a diopter of accuracy.

I just love high precision, specially on high index which makes for a thinner lens and that is about it.

When do you think in what year that the refractionist's will be able to make eye test's that are accurate to 100th of a diopter ? :hammer:

A high minus lens wearer is usually under corrected, so what is the use of these highly expensive free form lenses ?

Another hype to make labs buy the newer technology of surfacing equipment.

[scriptfiller]

What's the script? We have never had a pat. complain on 1.74's. They usually rave about the optical performance and obviously the thickness.

I'm waiting on Barry to chime-in on this thread, he has a very good understanding on how to fit the Auto II S.V.

[eyemanflying]

What are you talking about? It has always been Single Vision. Never wore a progressive. You can certainly get an Autograph II in SINGLE VISION. It is still front and backside digitally surfaced using eyepoint technology. Down to 1/100th of a diopter of accuracy.

It's not the material, the issue is in the design. I'm not a fan of Shamir FF whatsoever. Tell me, other than blind faith, how do you measure a lens to ensure 1/100th accuracy?

Maybe its off power by 0.03 of a diopter? Send it back for a redo. :p

[For-Life]

I just love high precision, specially on high index which makes for a thinner lens and that is about it.

When do you think in what year that the refractionist's will be able to make eye test's that are accurate to 100th of a diopter ? :hammer:

A high minus lens wearer is usually under corrected, so what is the use of these highly expensive free form lenses ?

Another hype to make labs buy the newer technology of surfacing equipment.

You should actually try a pair and then get back to us on that

[mshimp]

Sounds like the power is off. Maybe the doc. made an error? These would only be the reasons for the patients central vision to be blurred.

[Uncle Fester]

My first thought is a pressure problem when the lenses were chucked to edge.

P.S. I too thought the Auto 2 was a progressive and the sv is a digitally compensated Shamir design.

[Barry Santini]

There's alot on stuff to check here. Start with making sure your lab has supplied the correct Base Curve. My 1.74 Auto II SV FF were delayed because the proper BC (Shamir's program has very little tolerance here) was indefiniately Back ordered.

Barry

[Mr. Finney]

Probably the first thing you did, but have you closely inspected the AR where the lens was blocked to make sure it's not crazed?

[CuriousCat]

I too thought the Auto 2 was a progressive and the sv is a digitally compensated Shamir design.

www.shamirlens.com

[Robert Martellaro]

OC height was taken and used.

The vertical OC should be .5mm below the pupil per one degree of panto tilt. If the tilt is eight degrees, then the OC should be 4mm below the pupil. If you put the OC on the pupil, then try reducing the panto as much as possible. Reduce the dihedral (wrap/face) angle also. A -10.00 D lens with the OC central pupil, eight panto, and six wrap will be about half a diopter strong with a quarter cyl. Check the vertex distance also.

I had a situation like this recently where the vision in one eye was a tad soft. I couldn't clear the vision with hand held's placed over the eyeglasses, but was able to get better vision with a trial frame. Lens measured fine, but aspheric surfaces can measure correctly in a standard lensometer and still have optical errors. I made a new lens and that solved the problem.

[HarryChiling]

The vertical OC should be .5mm below the pupil per one degree of panto tilt. If the tilt is eight degrees, then the OC should be 4mm below the pupil. If you put the OC on the pupil, then try reducing the panto as much as possible. Reduce the dihedral (wrap/face) angle also. A -10.00 D lens with the OC central pupil, eight panto, and six wrap will be about half a diopter strong with a quarter cyl. Check the vertex distance also.

I had a situation like this recently where the vision in one eye was a tad soft. I couldn't clear the vision with hand held's placed over the eyeglasses, but was able to get better vision with a trial frame. Lens measured fine, but aspheric surfaces can measure correctly in a standard lensometer and still have optical errors. I made a new lens and that solved the problem.

I was under the impression that the Auto II SV's power was compensated for tilt?

[Barry Santini]

Sounds like the power is off. Maybe the doc. made an error? These would only be the reasons for the patients central vision to be blurred.

Why would it be a "doc" error?

Unless you're using just an autorefractor, then the patient/client is involved in the choosing of the lens, yes?

Please...no more "doc" errors...just like no more "12ths".

B

[For-Life]

Why would it be a "doc" error?

Unless you're using just an autorefractor, then the patient/client is involved in the choosing of the lens, yes?

Please...no more "doc" errors...just like no more "12ths".

B

true, but a huge part of it is communication on behalf of the professional. I have heard too many people tell me how the doctor just flashed up the lenses too quickly.

[Barry Santini]

I was under the impression that the Auto II SV's power was compensated for tilt?

Harry, yes, in a way. Basically, Shamir optimization in SV is sooo good that they (feel) that for most fiited/found POW value range, the lens's off-axis performance will meet and/or exceed a best form, CC SV lens..fitted correctly.

FWIW

B

[Robert Martellaro]

I was under the impression that the Auto II SV's power was compensated for tilt?

Nope. They don't ask for it, so we're on our own. Remember that thread a few months ago where we were banging our heads against the wall about this? What bothers me is that they're still asking for a vertical OC height to the he pupil instead of the height per Martin's Rule.

[Darryl Meister]

Lenses seem fine? I asked around and got an answer of, "1.74 is just not a clear

Any meaningful loss of clarity due to the quality lens material should be visible with a cosmetic inspection of the lens. The Abbe value of 1.74 isn't significantly different from the Abbe value of 1.67, so chromatic aberration wouldn't be an issue either way.

However, a lesser known phenomenon is the fact that as the refractive index of the material increases, the inherent curvature of the field aberration of the lens must also increase, which places additional optical contraints on lens designers. However, the optical differences between 1.67 and 1.74 high-index should be small.

Of course, you should inspect the lens for waves, verify the fit of the lens against the manufacturer's instructions, etcetera, if you haven't already. Also, if her central vision improves when the lens is tilted, this could indicate that there needs to be a better relationship between the power and the position of wear of the lens.

When do you think in what year that the refractionist's will be able to make eye test's that are accurate to 100th of a diopter

2007, with the advent of aberrometry combined with wavefront-guided vision corrections.

Basically, Shamir optimization in SV is sooo good that they (feel) that for most fiited/found POW value range, the lens's off-axis performance will meet and/or exceed a best form, CC SV lens..fitted correctly.

Just remember that prescription compensation primarily influences clarity through the central zone of the lens, while "best form" principles primarily influence clarity thorugh the peripheral zones of the lens. A lens design needs to consider both in order to completely maximize visual performance across the entire lens.

[skirk1975]

There's alot on stuff to check here. Start with making sure your lab has supplied the correct Base Curve. My 1.74 Auto II SV FF were delayed because the proper BC (Shamir's program has very little tolerance here) was indefiniately Back ordered.


Let me get this straight? If this is a true "Free-From" lens, then why do we have a base curve on backorder? Is it not "Created". I am under the impression that we start with a hunk of plastic and it is ground down? What is going on here ?

[Darryl Meister]

Let me get this straight? If this is a true "Free-From" lens, then why do we have a base curve on backorder? Is it not "Created".

Virtually all free-form lenses start with a semi-finished lens blank with a specified front or base curve. Only the back surface is generated using free-form surfacing.

[eyemanflying]

There's alot on stuff to check here. Start with making sure your lab has supplied the correct Base Curve. My 1.74 Auto II SV FF were delayed because the proper BC (Shamir's program has very little tolerance here) was indefiniately Back ordered.


Let me get this straight? If this is a true "Free-From" lens, then why do we have a base curve on backorder? Is it not "Created". I am under the impression that we start with a hunk of plastic and it is ground down? What is going on here ?

Most likely 100% back side free form. They use semi finished SV lenses for this. A $3 pair of blanks spun into $150.00. It's optical magic!

[skirk1975]

They use semi finished SV lenses for this. A $3 pair of blanks spun into $150.00. It's optical magic!

OK OK, hold on.....Shamir argues that that is all that Essilor does. Have a standard front and digital on the back. Their whole thing is supposed to be FRONT AND BACKside digital surfacing? What is going on here ? Conspiracy?