Convergence insufficiency

**Mikedp00** · 08-22-2011, 02:07 PM

With advancements in lens generators, the possibility of grinding BI prism in the seg area should be possible. Anyone aware of a lab that offers this service?

**gmc** · 08-22-2011, 03:10 PM

Originally Posted by Mikedp00

With advancements in lens generators, the possibility of grinding BI prism in the seg area should be possible. Anyone aware of a lab that offers this service?

Signet Armorlite (owned by Essilor) offers Kodak progressives with BI prism.

http://www.signetarmorlite.com/Marke...heet_FINAL.pdf

**braheem24** · 08-22-2011, 04:09 PM

You could also use an FT-45, executive, etc and prescribe BO prism in the distance and use the Distance PD for layout which will result with BI prism at near only.

**chip anderson** · 08-22-2011, 05:22 PM

Suppose someone should mention the Franklin Bifocal here. It's been possible to do this with these for about 260 years.

**Mikedp00** · 08-22-2011, 06:09 PM

Thanks Gary,

That is the information I am looking for. I will check them out.

**Mikedp00** · 08-22-2011, 06:12 PM

Thanks for the suggestion... I failed to mention that I was really looking or a PAL lens with prism in the seg.

**Mikedp00** · 08-22-2011, 06:13 PM

Nice TORCH Chip, but then I expected that from some of your other posts! My fault though, I failed to mention that I was really looking or a PAL lens with prism in the seg.

**Jacqui** · 08-22-2011, 06:34 PM

Just don't forget that when you grind prism onto a PAL (or any multifocal) you are going to get a narrower read area. This is because you are in effect tilting the lens. Why are you using a progressive?? People with convergence problems should have all possible read area.

**Jacqui** · 08-22-2011, 06:44 PM

Originally Posted by gmc

Signet Armorlite (owned by Essilor) offers Kodak progressives with BI prism.

http://www.signetarmorlite.com/Marke...heet_FINAL.pdf

Weren't these molded with the prism on the plus side and just used a SV freeform on the minus?? It should be possible to freeform these, but I don't think anyone that has yet. Software would need to be written and I don't think the programmers know how or why to do it.

Also the Signet/Kodak lens only went up to .75^ BI. It was really an anti-fatigue lens and not for convergence issues.

**rbaker** · 08-22-2011, 07:29 PM

With todays NC milling machines and tooling you can grind any configuration of lens surface. The problem will be the resultant visual acuity and functionality that is produced.

**Jacqui** · 08-23-2011, 08:35 AM

Originally Posted by rbaker

With todays NC milling machines and tooling you can grind any configuration of lens surface. The problem will be the resultant visual acuity and functionality that is produced.

I agree, Dick. The problem is that no one has done it yet. It should be possible for the right programmer to do and don't stop with just the base in and out, but also do base up and down for a slab off. I would do it myself, but I'm not a programmer of any sort.

**Diopterman** · 08-23-2011, 08:56 AM

You may want to talk with Michael Walach of Quest labs.

He will be the guy to tell you if it can be done and why or why not!

http://www.questopticallab.com/

**chip anderson** · 08-23-2011, 09:18 AM

Why do so many people think that if they sell a progressive they are providing the best vision possible for the patient?
How many of you have ever worn a bifocal or trifocal and an identical frame with a progressive interchangably?
Before you ask, I have and love my Ziess individuals, but for certian very small fine work (like painting and viening an artificial eye, I find the ST or SV designs give more precise detail. I would never give a progressive to a patient with sub-normal acuity a progressive and further compromise his acuity.

Chip

**OHPNTZ** · 08-23-2011, 09:50 AM

If a true CI, why not develop a vision therapy program for the patient?

**rbaker** · 08-23-2011, 10:20 AM

Originally Posted by Jacqui

I agree, Dick. The problem is that no one has done it yet. It should be possible for the right programmer to do and don't stop with just the base in and out, but also do base up and down for a slab off. I would do it myself, but I'm not a programmer of any sort.

The programming is the easy part. The lens design is where the cheese gets binding. Historically we can look at the work of Estelle Yancy and good old Doc Tillyer to see what the lens designer faces.