# Optical Forums > Progressive Lens Discussion Forum >  Progressive with high prism

## Jalane

I have a patient who currently wears a Varilux Comfort DRx with 8D base out OU.  With her new script, the prism is now 13D base out OU.  Our lab is telling us that that amount of prism is too high for a progressive.  I am reluctant to put the patient in a FT28 because of her balance issues.  Our lab is telling us that the best option for this patient is single vision.  I know there has to be a lab out there with the expertise to be able to do her new script with the prism.  Her distance Rx is very mild, but she does have 25D esotropia.  Any help will be appreciated.

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## mervinek

That's quite a shift.  Did you try a fresnel first?  Just curious when the change is so great.

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## Jalane

Fresnel goes in 5D increments after 10D, so not an option.  I can get a 12D, but I don't think the Dr wants to back down on the prism due to the big shift in patient's esotropia.

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## Optical Roy

You could induce the split prism, then place a fresnell over the non dominate eye in the amount that is needed to create the overall prism effect., That should make it a 10d fresnell for the non dominate eye going with the current 8D base out OU in the current rx.

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## Robert Martellaro

13∆ total? That's doable on a semi-finished Comfort. Some labs will try it on a freeform generator but the results vision-wise are typically very poor. 

Make sure to check (likely) the need to modify the IPD to anticipate the eyes turn towards the prism apex by .3mm per prism diopter. 

Keep auxiliary segmented or SVNO on the table for those with above average close tasks.

Use small, round frames that will accommodate increased levels of prescribed prism in the years ahead.

Hope this helps,

Robert Martellaro

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## Jalane

26 total prism.  13 out in each eye.

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## Robert_S

26 is a lot for a progressive tbh.

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## Robert Martellaro

> 26 total prism.  13 out in each eye.


Ouch. Fresnel then, if a PAL. The highest I've gone is a pair of -8's with 16∆ out total, but in SVDO with Chemistrie power clip over for near. 

Best regards,

Roberts Martellaro

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## jefe

From my conversation with the rep at the Luxexcel booth at VEE a couple years ago, that's the sort of thing they will be able to make using a 3D printing process.  As I recall, they're doing some limited processing at a lab in NC.

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## drk

> Make sure to check (likely) the need to modify the IPD to anticipate the eyes turn towards the prism apex by .3mm per prism diopter. 
> 
> 
> Robert Martellaro


You are so good at this stuff, Robert.  


OK, let's flesh out your recommendation.   This whole exercise is how to convert monocular p.d.s taken with a pupillometer-accuracy-level device, with ALTERNATE OCCLUSION of the fellow eye (that is, not measuring it in the binocular state).

Let's say someone has the more typical 2^ in each eye.   Let's say it's BI.

So you're saying that the inset needs modified for the progressive corridor and near zone.

It is true that prism allows the eye to go towards its rest position.  In the case of an exo deviation as is the case in the example, each eye would want to go 2^ out (which isn't an angular or linear amount, but you've converted that to a linear amount at the spectacle plane...0.3mm per prism diopter).  

Therefore we would outset the whole lens via the p.d. (if single vision, segmented, or PAL) by 2^ X 0.3mm = 0.6 mm/eye.

That's within measurement error for low prism amounts.  




Take the example to a less common amount, say, 6^ BO OU.

6^ x 0.3mm = 1.8mm inset per eye.  That is not insignificant.  



I have not done this, ever.  Shame on me.

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## Kwill212

Yes Drk. This is laid out and explained in chapter 20 of Systems for Ophthalmic Dispensing 3rd edition. 

The summary table can be seen here along with the table describing how and when to alter the amount of prescribed prism, which is described in detail in the preceding pages. 

https://www.google.com/books/edition/System_for_Ophthalmic_Dispensing_E_Book/sV5PAQAAQBAJ?hl=en&gbpv=1&dq=system+for+ophthalmic+dispensin  g+box+20-4&pg=PA486&printsec=frontcover





> Therefore we would outset the whole lens via the p.d. (if single vision, segmented, or PAL) by 2^ X 0.3mm = 0.6 mm/eye.
> That's within measurement error for low prism amounts.



For a PAL it is important to keep the eye path in the corridor to receive the most usable area of an already narrow mid range view. Not adjusting the PD for prism displacement will reduce the usable int/near area, regardless if it within measurement error for low prism amounts.

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## drk

I like it!

Screenshotted it.

Funny that Brooks and Borish's conclusion used some of the same ideas and numbers I did!

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## drk

OK, here's where I go nuts....Do labs already do this automatically?  What about digital lens softwares?

In general, if it's a software-based lens, I don't monkey.  If it's a "grinder" then I'm the software.

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## Kwill212

There is no lab or lens software that I am aware of that will do this automatically for you.

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## Robert Martellaro

> OK, here's where I go nuts....Do labs already do this automatically?  What about digital lens softwares?


No, and no. 

Dick Cook at Benson Optical Co., circa late 80's, showed me why my segment heights were misaligned when there was prescribed vertical prism. 10∆ vertical on a segmented is 3mm off, more if there is physical asymmetry in the facial structure. I could see the error from across the room, not just sitting face-to-face at the dispensing table. 

Best regards,

Robert Martellaro

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## Lensman11

There is no free form generator that can handle that amount of prism. Actually they have problems with more than 2 diop of prism. Usually you have to block in the prism and not ask the generator to produce it when above 2.  If you want to be creative and actually have a blank thick enough to accommodate this amount of prism it could be done by first grinding the progressive design on the back of the lens and then grinding the prism on the front. Most labs do not have the tooling or equipment to process convex curves but some do and this could be done.

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## Jason H

Oi, the research is sound and in a real world application it absolutely works. I work for a lab - if we did it automatically there would be nothing but remakes. I have accounts that are aware and use the concept. The vast majority would consider it a lab error.

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## Jalane

I know.  Patient was wearing 8 base out OU successfully in a progressive.  We have a lab that can do in in 1.74, but the patient would need to go to a 48-50 eye size frame.  Patient has a large face/head and that frame size is way too small.  I'm working with the prescribing doctor to see of we can come up with a solution that will make both the patient and doctor happy.

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## Jalane

Patient currently wears 8 Out OU for a total of 16.

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## Quince

> I know.  Patient was wearing 8 base out OU successfully in a progressive.  We have a lab that can do in in 1.74, but the patient would need to go to a 48-50 eye size frame.  Patient has a large face/head and that frame size is way too small.  I'm working with the prescribing doctor to see of we can come up with a solution that will make both the patient and doctor happy.



Hate to say it- but Oakey works wonder for finding a smaller eye size (51ish) with accommodating for a wide fit. The bowing in the temples has been a life saver for me with certain fathead/ high Rx combos.

Ovvo is a great line for a small eye size but stretchy fit. The lens will always be much more visible though. (I did a -20.00 years ago that worked out well.)

Please post a photo of the outcome if you can. I'm sure many on here would be intrigued with that amount of prism. I don't think I've seen anything over their original strength of around 16 total.

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## Robert Martellaro

> I know.  Patient was wearing 8 base out OU successfully in a progressive.  We have a lab that can do in in 1.74, but the patient would need to go to a 48-50 eye size frame.  Patient has a large face/head and that frame size is way too small.  I'm working with the prescribing doctor to see of we can come up with a solution that will make both the patient and doctor happy.





> Jalane
> 26 total prism. 13 out in each eye.


Two points: 1) The wearer will lose two to three lines of VA with low abbe materials, about the same they would experience with a Fresnel, except with the latter they will only lose VA in one eye. 2) If a PAL, you'll need to increase the decentration by about 3mm per eye. Make sure your lab knows this because a smaller eye size will probably required, depending on the dioptric power, probably in the 42mm to 44mm range, or use lenticularization. 

Best regards,

Robert Martellaro

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## Uncle Fester

I'd be really tempted to make a simple sv distance rx into her frame at cost (or roll it into the charges) to be sure this complicated expensive job for her doesn't turn into an expensive complicated job for me too.

Trial frames and real world frames & lenses are usually the way to go, but this has red flags flying!!!

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## Jalane

I agree about the red flags!  I discussed going to SV distance and readers, but she really is adamant about keeping her progressive.

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## Jalane

After speaking with the prescribing doctor, we are going to try lenses without any prism to see if she can adapt to the esotropia with suppression scotoma.  If she cannot adapt, its back to the drawing board. :Unsure:

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## opticalallusions

Is strabismus surgery an option for the patient?

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## Jalane

Strabismus surgery not an option.

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## Jalane

Strabismus surgery is not an option for this patient.

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## Jalane

Patient picked up her new glasses without any prism.  The diplopia is still present, but not as pronounced as we thought it might be.  She tolerates it better with her polarized sunglasses than with the clear lenses.  She is being referred to a neuro-ophthalmologist by her regular ophthalmologist.

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## Uncle Fester

Thanks for the follow up.

Will your Doc still be in the communication loop?

If possible it would be great to hear what the top dog recommends.

Kind regards,
Fester

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## Jalane

Yes, the original doc will still be in the loop.  I will post further updates as I receive them.

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