specifying center thickness

**jamie w** · 09-29-2009, 12:48 PM

can anyone help me understand specifying center thickness on progressive lenses I got a job back from the lab today the pt rx was -5.00-2.00 with a +2.25 add ou. Pt previously wore a panamic in poly. My initial thought was 1.67 would be a better choice. I really like using the Definity so this is the combo I went with. The patient was and I were disappointed to see that the lenses were actually thicker than her previous pair. The eye size and dbl are similar in the two frames. I measured center thickness come to find out her old pair was a 1.0CT and the Definity was a 2.0CT, hence we have thicker lenses.
Can anyone give me some advice on specifiying CT, what are the FDA specifications? The person at the lab was only able to tell me that on "digital lenses you can not specify BC or CT". However, I just got an physio 360 in 1.74 with a 1.0 CT last week????
please help
thanx jamie

**Aarlan** · 09-29-2009, 12:50 PM

I can see not being able to specify BC, since they have supposedly mapped out the optimum curves, but not being able to specify CT? that's odd...so no 3.0 safety in digital lenses?

AA

**Spexvet** · 09-29-2009, 01:40 PM

The 1mm difference in center thicknesses will result in an edge thickness difference of 1mm. Any greater difference is caused by something else - probably size.

**jamie w** · 09-29-2009, 02:01 PM

I realize that the diffrence will only be 1mm, however this is relative the point is the pt notices! So am I better off using a 1.67 which I thought would create a thinner edge. Can I specify a 1.0CT on a 1.67,if so can I get this in a digital or conventional progressive?

**Uilleann** · 09-29-2009, 03:49 PM

Was the original pair a full frame or drill mount, and the new frame a groove (semi-rimless)???

1.74 would again offer the best cosmetic appearance regarding thinness - but that must be paired with the appropriate frame. I would take some careful measurements of the previous frame dimensions and PD/OC. Compare that to what you have now. And ask to talk to the lab manager - see what you can work out together for the thinnest lens option in this case.

:cheers:

**jamie w** · 09-29-2009, 04:38 PM

The previous glasses were also a metal frame and eyesize and bridge size are the same. I spoke with the lab manager at another lab we use and he was much more helpful. I was told that I can get a 1.67 with no less than a 1.5 CT especially when AR is involved. I am to assume that whomever made the previous pair should not have used such a thin CT. I think I will stick with 1.67 and use a lens that is not digital(which is not my first choice)so I can specify a 1.5 CT and hope the pt is happy with the results.

**Uilleann** · 09-29-2009, 05:31 PM

Jamie,

You stated you've gotten other jobs back in 1.74 with a 1.0 center correct? Have you explored that option as well?

**jamie w** · 09-29-2009, 05:38 PM

actually that job was done by the same lab I was talking to today and we did touch on that particular job. He was very suprised and concerned that they may have ground lenses with a 1.0CT in a 1.74. So he called the manufacturer and apparently essilor ground the lenses with that CT so according to him they accept all responsibility for any liability. He did not reccomend doing that in the future and stated that his lab would only grind 1.67 and above with a 1.5CT

**Uilleann** · 09-29-2009, 05:42 PM

What is the eye size, bridge and mono PD of this job/frame??

**jamie w** · 09-29-2009, 05:50 PM

uliean,
the eyesize is 48,dbl 18 mono pd 28.5/29.0

**Uilleann** · 09-29-2009, 06:13 PM

two L's, two N's. hehe

That seems like a pretty narrow PD for that eyesize and Rx power. If you can manage to fit your pt. with even a 46, it should help noticeably.

My lab guy is out till Thurs., but I'm curious to pose your problem to him and see what he says about center thickness as well. I can let you know if you'd like. Lemme know. :cheers:

**jamie w** · 09-30-2009, 09:02 AM

ideally a 46 eyesize would create a thinner edge and you and I both understand this, however look at things from the pts perspective. Her comment to me was "why should I pay more for a thinner material and my lenses are thicker than my previous lenses." Considering the fact that the eyesizes are the same and the bridge on the old frame is actually 1mm less I can understand her frustration. I would be interested to know what your lab guy thinks. I would like to be as educated as much as possible especially if I tell her that whomever made the old lenses should have never made them so thin.