# Optical Forums > Progressive Lens Discussion Forum >  Help troubleshooting Progressives with Prism

## nclairmore

Rx:
OD -3.00 -0.50 x168  4Out
OS -2.50 -0.50 x014  4Down

Add: 2.00

Pt is wearing a physio enhanced poly.  Lenses are made with OD 2 out 2 up, OS 2 out 2 down.

When comparing monocularly, pt feel that "sweet spots" for reading are different by about 2 inches at reading distance: 2 inches higher out of the right than the left eye.

Also, pt feels that the seg itself is slightly high.  Distance vision is best if he drops his chin slightly.  There is no difference in "sweet spot" height in the distance.

Currently the segs are measured at the same height OU.

I thought about dropping the seg in his right eye by about 1mm, hopefully making the distance better out of that eye and better aligning the reading sweet spots.  However, I do not believe that OS pupil is actually physically higher than his OD.  This would be a cheap, kind of guesswork fix.  Nonetheless, one I contemplated, though one I probably won't pursue.

I feel like the problem is a result of the prism.  I am unsure of how to approach the situation if that is the case, outside of an Rx check.  

I also blame poly.  I did not do the original order, and poly would not have been my material of choice in this rx.

Outside Info: we are talking about a drill mount Tag Heuer frame, and the pt just happens to be an OD.

Any opinions on this matter would be greatly appreciated.  Cheers!

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## uncut

Welcome to the forum, nclairmore!   Great first post.

This will be my short coffee-break answer:

While it is accepted practice to split prism.....in some cases, it might be purer to avoid, due to side-effects.   It sounds like this a "new" prism situation?     

If it is, *produce the prism purely as prescribed*.   At very least split only in one direction.  I will expand on this later.  This is primarily due to a multifocal being used to create the optical device, the index chosen, the add power, and the RX.

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## uncut

> Rx:
> OD -3.00 -0.50 x168 4Out
> OS -2.50 -0.50 x014 4Down
> 
> Add: 2.00
> 
> Pt is wearing a physio enhanced poly. Lenses are made with OD 2 out 2 up, OS 2 out 2 down.
> 
> *When comparing monocularly, pt feel that "sweet spots" for reading are different by about 2 inches at reading distance: 2 inches higher out of the right than the left eye.
> ...



The highlighted statement would only be important as a complaint if the same condition exists binocularly.  Phenomena noted *monocularly is sometimes normal!*

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## nclairmore

uncut, 

Thanks for your response! I have learned alot from you in my lurks around the forum.

The prism is not new, neither the PAL.  I still like the "purely as prescribed" idea and look forward to reading further about that.

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## Robert Martellaro

> Rx:
> OD -3.00 -0.50 x168  4Out
> OS -2.50 -0.50 x014  4Down
> 
> Add: 2.00
> 
> Pt is wearing a physio enhanced poly.  Lenses are made with OD 2 out 2 up, OS 2 out 2 down.
> 
> When comparing monocularly, pt feel that "sweet spots" for reading are different by about 2 inches at reading distance: 2 inches higher out of the right than the left eye.
> ...


With prescribed prism, our eyes will rotate towards the apex by about .3mm per prism diopter (light is deviated 1cm at a distance of one meter- the distance from the center of rotation of the eye to the cornea, about 15mm, plus the vertex distance, about 13mm, averages about 28mm (the stop distance), hence a deviation of .28mm per diopter of prism). 

In your example, you would want to use dissimilar fitting heights to keep the progressive optics aligned with the eyes. You said that the fitting height is the same when measured without the prism in place, so if that value is, for example, 20mm, you should order OD 19.5 and OS 20.5. Do the same for the PD, cutting each eye by .5mm.

Hope this helps,

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## uncut

Now for the liquid lunch/sandwich post:

Robert has added some food for thought!  Excellent!

The use of prism technically is required by only one of the eyes..........but, for cosmetic reasons, ease of production, and weight inbalances, we try to split the results, often creating new mechanical and behavioral requirements.    

First, evaluate existing prism amounts, in both lenses worn,* in situ.*  Listen carefully, and ask questions about prism function, and interferences.  Note preferences, in head tilt, excursion deviation, near point preferences, and occupational requirements.

Prism is max values in SV powers, only............and unless the examiner has trial framed the patient, or over-refracted with hand held prism......the fuctionality of the values prescribed, may only be suited for SV distance, and need to be modified for all other devices.

In your case you might find that splitting it vertically, might be acceptable to the patient, mostly in the distance part of the multifocal, I would try placing the horizontal prism, all in the O.D. Rx, I would only apply this for the multifocal. 
 My ancecdotal concept is that the patient, would only increase the thickness of the O.D. lens, yet not significantly, placing it, in front of the eye requiring and leaving the eye *not requiring it* to deal with less prism, and create more fusion of images for intermediate and near.  If you feel that you would not be comfortable with dissimilar seg heights, as Robert pointed out,  you could also split the prism differently, vertically, like 3 vs 1, as opposed to 2 and 2................

Back to the grindstone..............the mill whistle has blown!

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## Uncle Fester

Oopps- My ignorance is showing again!  :Redface: 

excursion deviation?
How much the eyes move while looking through the corridor??

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## uncut

> Oopps- My ignorance is showing again! 
> 
> excursion deviation?
> How much the eyes move while looking through the corridor??


Yes, there, too.............

But I was" blanket-like " trying to describe excursion(field of view) difficulties encountered by the wearer, due to index of refraction of material chosen, lens power, DOC placement, and prism values, increasing and decreasing therein. in device, whether SV, BIF or Multi.  This phenomena is not the same vertical, or horizontal, or obliquely, and is unique to each patient.

It might call for a better word/phrase?

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## optilady1

I have nothing to add to this thread other than this: The stuff you people know here is amazing!

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## Uncle Fester

> Yes, there, too.............
> 
> But I was" blanket-like " trying to describe excursion(field of view) difficulties encountered by the wearer, due to index of refraction of material chosen, lens power, DOC placement, and prism values, increasing and decreasing therein. in device, whether SV, BIF or Multi.  This phenomena is not the same vertical, or horizontal, or obliquely, and is unique to each patient.
> 
> It might call for a better word/phrase?


Thanks- I've covered it back up.  :Tongue: 

All I could picture were the eyes out for a Sunday stroll!

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## uncut

> Thanks- I've covered it back up. 
> 
> All I could picture were the eyes out for a Sunday stroll!


Perhaps a utube video, not unlike the Essilour Rep, or the Sales Rep(Prada one) :Bounce: ,....might be in order?

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## Robert Martellaro

> Oopps- My ignorance is showing again! 
> 
> excursion deviation?
> How much the eyes move while looking through the corridor??


Redundant, as in "crooked politician".

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## junebuggy

Robert-if I ever have to move back to the Milwaukee area I would love to shadow you.

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## sharpstick777

Although this thread is informative, I think we forgot the patient?  

nclairmore, welcome to Optiboard and thanks for sharing!

As you surmized, Poly is not best for this RX.

You didn't share the patients distance visual accuity?  DVA is crucial for solving this issue, you mention that DVA is good if he drops his head 1mm, but you didn't say whether is was good just centrally or across the entire lens.

The Physio Enhanced is a hybrid design which means the front blank is the same as the Physio, and the back is "Ehanced" digitally.  The problem (among others) with this dual design is that both front and back must line up perfectly, as there is essentially two design surfaces, one cast on the front and one digital on the back.  If you hold up both your hands, and make circles with each hand, you can see through them when they are lined up.  Move one hand slightly (so the circles don't line up) and you will very quickly shrink your clear zone.  Prism will cause the front and back surfaces not to line up.

If actual DVA is good and matches the refraction,even with his head tilted down, then you have lens design issue which is hurting binocular symmetry.  If DVA is good only centrally, but not peripherally, then prism may need to be adjusted.  If DVA is only OK and doesn't match the refractive expected DVA, then the RX might need to be adjusted.  Of course, get OUT of Poly with this much prism.  

I would recommend 1.60 for your patient.

I would also recommend one of the 100% free-form lenses that have a spherical front, and adjust the corridor for prism.  There are two right now, the Zeiss Individual 2 and the Seiko Surmount.  The Autograph 3 will also have this feature, but its not out till late March.  In both of those lenses the corridor is realigned to keep it centrally located to improve how the eyes work together in the lens.

In my opinion, its most probably the lens choice.




> Rx:
> OD -3.00 -0.50 x168  4Out
> OS -2.50 -0.50 x014  4Down
> 
> Add: 2.00
> 
> Pt is wearing a physio enhanced poly.  Lenses are made with OD 2 out 2 up, OS 2 out 2 down.
> 
> When comparing monocularly, pt feel that "sweet spots" for reading are different by about 2 inches at reading distance: 2 inches higher out of the right than the left eye.
> ...

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## Robert Martellaro

> Robert-if I ever have to move back to the Milwaukee area I would love to shadow you.


When I was younger, I enjoyed traveling to other offices to fill in for vacations and illnesses. I learned a lot, mostly good, about how other opticians managed some of the more challenging aspects of our occupation. Stop in and say hi if you're in my area, or give me a heads-up if you want to sit down and talk optics.




> Although this thread is informative, I think we forgot the patient?


I believe I offered a pretty darn good explanation, base on science and experience, that matched the symptoms. The rest is up to nclairmore, and from what I've read, the patient seems to be in good hands. 




> The Physio Enhanced is a hybrid design which means the front blank is the same as the Physio, and the back is "Ehanced" digitally. The problem (among others) with this dual design is that both front and back must line up perfectly, as there is essentially two design surfaces, one cast on the front and one digital on the back. If you hold up both your hands, and make circles with each hand, you can see through them when they are lined up. Move one hand slightly (so the circles don't line up) and you will very quickly shrink your clear zone. Prism will cause the front and back surfaces not to line up.


I'm not sure if you're saying that the manufacturers have to be more diligent when the Rx includes prescribed prism, or that Hoya and Essilor can not do this properly, and that we should only use semi-finished PALs or full backside designs for prescribed prism Rxs.

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## sharpstick777

Anytime i provide design elements on two surfaces vs one, alignment of those designs is crucial to success.  Prism could potentially misalign those designs esp in a thicker lens, the effect then would be narrower fields of view.




> I'm not sure if you're saying that the manufacturers have to be more diligent when the Rx includes prescribed prism, or that Hoya and Essilor can not do this properly, and that we should only use semi-finished PALs or full backside designs for prescribed prism Rxs.

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## nclairmore

Sorry about my delayed response!

Robert, your original post was very informative.  I found http://www.2020mag.com/ce/TTViewTest...essonId=105838 that touches on that topic toward the end of the article (~.33 mm rotation toward apex per diopter of prism)

sharpstick also was helpful.  Your point makes sense, and your illustration was helpful.  Are you suggesting that a traditional physio would be better than the physio enhanced because of the hybrid design on the enhanced?  I may go with the Auto 3 when it comes out.  Also, distance was clear for the majority of the lens.  Not quite edge-to-edge, but better than he expected (as long as his head was tilted slightly down, as stated earlier) 

After all of this, the Dr. decided to re-refract himself and wait before we remake his lenses.  Thanks everyone for your responses! I appreciate all of the feedback.

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## nclairmore

another, more general question about this topic:

When we use prism thinning in progressive lenses, the eye will rotate about .33mm down per diopter of BD prism.  In a strong add, this could result in nearly 2 diopters of BD prism, which would rotate the eye by ~.66mm.  In this case, should we adjust the fitting height to accomodate for this rotation?  ie. change the measured seg from 20.0 to 19.5

I think the answer is yes, I am just testing my understanding.

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## Robert Martellaro

> another, more general question about this topic:
> 
> When we use prism thinning in progressive lenses, the eye will rotate about .33mm down per diopter of BD prism.  In a strong add, this could result in nearly 2 diopters of BD prism, which would rotate the eye by ~.66mm.  In this case, should we adjust the fitting height to accomodate for this rotation?  ie. change the measured seg from 20.0 to 19.5
> 
> I think the answer is yes, I am just testing my understanding.


Yes. However, I would concentrate on any differential in heights instead of absolute heights, although it makes sense to round up if you get an in-between measurement. Note that in your original example, prism thinning would not be needed due to the minus distance power.

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## nclairmore

> Note that in your original example, prism thinning would not be needed due to the minus distance power.


I understand.

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## Quince

So we had a similar situation in my office last week and I'm hoping to be enlightened. Robert seemed to touch on what I'm hoping to understand. Here we go:


+3.25   -1.00   x088     3BU   3BO
+6.00   -2.75   x074     3BD   3BO
+2.00 ADD     PD 31ou    Seg 28ou

1st pair was ordered uncut and finished in house. 2nd pair was safety so we sent frame to lab and received job complete. 

The job we received measured 28/30 for the segs. Everything else was dead on. Lab redid the job but have been trying to tell us that this seg differential was not a mistake and should have been passed. 

The patient is happy with the final product of both pairs, so my goal now is to figure out if we are missing something here that we should be applying. Any insight is appreciated!

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## Robert Martellaro

> So we had a similar situation in my office last week and I'm hoping to be enlightened. Robert seemed to touch on what I'm hoping to understand. Here we go:
> 
> 
> +3.25   -1.00   x088     3BU   3BO
> +6.00   -2.75   x074     3BD   3BO
> +2.00 ADD     PD 31ou    Seg 28ou
> 
> 1st pair was ordered uncut and finished in house. 2nd pair was safety so we sent frame to lab and received job complete. 
> 
> ...


Quince,

The lab should not compensate for the anticipated deviation of the eyes due to vertical prism. That's the dispensing optician's responsibility, without exception. If you order 28 high in both eyes, that's what you should get. 

A level fitting height with this Rx would be normal if the right eye is about 2mm higher than the left eye because the right eye will turn down due to the BU prism, and left eye will turn up due to the BD prism, each by about 1mm. 

The horizontal fitting position should also be adjusted for the BO prism (.3mm x 6∆ = 1.8mm...reduce the IPD by 1mm per eye).

Due to anisometropia, if the PRP/180 line of the selected PAL design is not coincident with the fitting cross, the "drop" will induce vertical prism imbalance- BU in the right, and BD in the left, increasing the prescribe vertical prism by about one prism diopter. For example, a 4mm drop will induce 1.1∆ BU Rt or 1.1∆ BD left. (.4cm x 2.75 D). Reducing the prescribed prism 6∆ to 5∆ total BU Rt. would be recommended.

Hope this helps,

Robert Martellaro

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## Quince

Robert, thank you very much for your reply. I hope I'm understanding this correctly.

If you were to fit this patient, you would have originally ordered with a 2mm difference in seg heights to compensate for the effect of the prism. OR set all the the vertical prism in the OD and lessened it by 1 diopter (of prism). 

I have never combined prescribed prism after receiving an RX with it already split. Is this something that you would do in other scenarios as well?

Also I wasn't sure how to utilize this suggestion: "*The horizontal fitting position should also be adjusted for the BO prism (.3mm x 6∆ = 1.8mm...reduce the IPD by 1mm per eye)*."
Are you referring to the Intermediate PD? If so, I have never specified any adjustments to this measurement in a PAL. At what stage in lens processing would this be applied?

Thanks again for your words of wisdom!

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## Robert Martellaro

> Robert, thank you very much for your reply. I hope I'm understanding this correctly.
> 
> If you were to fit this patient, you would have originally ordered with a 2mm difference in seg heights to compensate for the effect of the prism.


Yes, if their eyes are level. 




> OR set all the the vertical prism in the OD and lessened it by 1 diopter (of prism).


 Split (see below).




> I have never combined prescribed prism after receiving an RX with it already split. Is this something that you would do in other scenarios as well?


I almost always split the prism, for both cosmetics and visual acuity (chromatic aberration). The split might not always be 50/50. For example, if the degree of prism is high, and one eye has poor BCVA, I might put more prism in that eye.

Do not spit the prism if the Rx says "do not split prism" or "fill exactly as written". Call the prescriber to verify.




> Also I wasn't sure how to utilize this suggestion: "*The horizontal fitting position should also be adjusted for the BO prism (.3mm x 6∆ = 1.8mm...reduce the IPD by 1mm per eye)*."
> Are you referring to the Intermediate PD? If so, I have never specified any adjustments to this measurement in a PAL. At what stage in lens processing would this be applied?


Interpupillary Distance = IDP = PD.

Go to post five for an explanation. Also see "The Effect of Prescribed Prism on Progressive Lens Fitting" System for Ophthalmic dispensing 3rd Edition -Brooks/Borish (page 482).

Example: Plano Sphere Rt 6∆ BO Lt 6∆ BO. PAL. IPD 32/32. Each eyes turn nasally 2mm due to the prescribed prism. Order 30/30 so that the fitting cross is aligned with the visual axis, improving overall performance, especially at near.




> Thanks again for your words of wisdom!


Your welcome. Good luck with your lab- it might be a problem with the blocker, but that's not my area of expertise.

Robert Martellaro

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## Quince

I will look up what you have notated for me. I only run conventional so this one was sent out for digital processing but this sounds like something I want to read into further for future cases. Reading up on prism is fresh in my mind from ABO studying so I figure now is the time!

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## Pete Hanlin

Love reading threads like this- nice to know there is still a wealth of dispensing knowledge out there!

One more consideration from the design perspective (based on my own dispensing experience)...  I found relatively "hard" designs work well for patients with prism, because these designs tend to have a better defined "sweet spot" which a.) creates a "locator" for the eyes and b.) allows the patient to describe any misalignment of the sweet spots (as was noted in the OP).  
To be honest, the best results I achieved for patients with prism were with the ultimate in "hard" designs- _blended bifocals_ (let the flaming begin :^).  By adjusting the fitting height and inset, I could usually provide very comfortable distance and near vision without a line (and, at least in my experience, intermediate vision is always a crap shoot for these patients anyway).  With a few exceptions, progressive designs challenge binocular vision anyway- and someone with prism doesn't need additional challenges (IMO).  If the patient did a ton of work at the computer, I'd recommend and fit blended lenses with the intermediate entered as the distance script and half the ADD for near (even for patients without prism, this set-up works great for computer lenses). 

Disclaimer- Essilor employee... If I were selecting a lens from the Varilux portfolio for the scripts mentioned in this thread, it would be either a traditional Varilux Comfort or a Varilux Comfort DRx (most likely the former) in 1.60.  While I love multi-surface designs, I agree with _sharpstick777_ that this amount of prism might be better suited to a single surface design.

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## Quince

Good to know about the preference for hard designs. I will keep that in mind. 

Personally, I love the Duo. I've also had really good luck using them for PAL nonadapts or patients needing temporary multifocals. We've also had success with using either the Duo or anti-fatigue designs as PAL training wheels. 

I try and get as much of an understanding of these kinds of concepts as I can because I am seeing it from all sides. As a surfacing tech and optician I often have the upper hand of lab knowledge assisting my ability to fit patients, but this one had me stumped. 

Won't be the last time! 

And if I didn't like it, I'd be in the wrong field  :Cool:

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## Robert Martellaro

> Love reading threads like this- nice to know there is still a wealth of dispensing knowledge out there!
> 
> One more consideration from the design perspective (based on my own dispensing experience)...  I found relatively "hard" designs work well for patients with prism, because these designs tend to have a better defined "sweet spot" which a.) creates a "locator" for the eyes and b.) allows the patient to describe any misalignment of the sweet spots (as was noted in the OP).  
> To be honest, the best results I achieved for patients with prism were with the ultimate in "hard" designs- _blended bifocals_ (let the flaming begin :^).  By adjusting the fitting height and inset, I could usually provide very comfortable distance and near vision without a line (and, at least in my experience, intermediate vision is always a crap shoot for these patients anyway).  With a few exceptions, progressive designs challenge binocular vision anyway- and someone with prism doesn't need additional challenges (IMO).  If the patient did a ton of work at the computer, I'd recommend and fit blended lenses with the intermediate entered as the distance script and half the ADD for near (even for patients without prism, this set-up works great for computer lenses). 
> 
> Disclaimer- Essilor employee... If I were selecting a lens from the Varilux portfolio for the scripts mentioned in this thread, it would be either a traditional Varilux Comfort or a Varilux Comfort DRx (most likely the former) in 1.60.  While I love multi-surface designs, I agree with _sharpstick777_ that this amount of prism might be better suited to a single surface design.


Pete,

From my experience, and from consultations with other experts, the harder design PALs were the design of choice for the high astigmatic Rxs, where the prescribed (edit-astigmatism) would interfere less with the unwanted astigmatism of the PAL design, resulting in less deformation of the corridor and near zones. The extra wide near zone helped also. This was before we had Zeiss and Rodenstock atoric PALs, presently the surface design (atoric/optimized) of choice for moderate to high astigmats.

I believe the only advantage of a hard design with prism Rxs is from the increased near zone width, improving near performance when the lens was not fit optimally, that is, when not accounting for the eye turn from the prescribed prism.

Your spot on with the use of 1.60 Varilux Comfort or New Comfort (standard corridor length) semifinished PALs for moderate to high values of prism (> 4∆ total), because it works, where free-form/optimized designs are almost always instant failures. I will occasionally use Trivex Physio where safety is a chief concern and the near vision sees light use or is shared with task SVNO eyeglasses.

Best regards,

Robert Martellaro

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## Becca217

Any advice appreciated for a patient who wants a PAL & transitions.
-0.50  SPH          add 250 5.5 BD 5.5 BO 
Plano-1.00x140 add 250 5.5 BU 5.5 BO
Right orbit is 2mm higher

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## Robert Martellaro

> Any advice appreciated for a patient who wants a PAL & transitions.
> -0.50  SPH          add 250 5.5 BD 5.5 BO 
> Plano-1.00x140 add 250 5.5 BU 5.5 BO
> Right orbit is 2mm higher


 Dispensed about 4 weeks ago, seen today for an additional pair with FT28s. I also made SVRO (sans prism) to go with the SVDO.  

-0.75 +1.00 x 105 7.5 OU 5.00 UP
-0.75 +0.75 x 065 7.5 OU 5.00 DN
Add +3.00

Frame is 42mm eye 24 dbl B 30.5. I'll try to remember to get a photo of the unequal segment heights and increased inset of the forthcoming segmented multifocals.

Client was previously wearing PALs with Fresnel OS, and SVRO without prism. Poor near and far VA. Significant improvement in vision with the above. IME, too much prism for a PAL, especially oblique prism, but if you must, use a well designed semifinished PAL, high Abbe materials, and position the optics in anticipation of the eyes deviating towards the prism apexes by .3mm per prism diopter. 

Hope this helps,

Robert Martellaro

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## Tallboy

Robert who makes that frame you posted?

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## Robert Martellaro

> Robert who makes that frame you posted?


Eye Think Eyewear out of Chicago. NOS (new old stock) made in France. Stainless Steel. It's about the only way to find a "medical", non-urbanized (clean lines, simple colors) frame in this size (wide dbl, deep B, narrow A). If you run across anything like this give us a heads-up. 

Hope this helps,

Robert Martellaro

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## drk

> and position the optics in anticipation of the eyes deviating towards the prism bases by .3mm per prism diopter.


Robert, this is new to me.  I'm not sure I agree, here, regarding direction.

I can understand at some level, but will you break down your reasoning, please?

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## Kwill212

> and position the optics in anticipation of the eyes deviating towards the prism bases by .3mm per prism diopter.


Isn't the deviation _away_ from the prism base?

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## Robert Martellaro

> Robert, this is new to me.  I'm not sure I agree, here, regarding direction.
> 
> I can understand at some level, but will you break down your reasoning, please?





> Isn't the deviation _away_ from the prism base?


Fixed. I need a proofreader, especially after drinks before dinner, wine with dinner, and after dinner drinks. 

Best regards,

Robert Martellaro

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## Robert Martellaro

More...

https://www.optiboard.com/forums/sho...escribed-prism

Continued at sci.med.vision

https://groups.google.com/forum/#!to...on/1UFTTgQX1IA

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