Prisms prisms prisms

[RetroRat]

We are currently working out a plan of attack for a 35yo male px with a neurological condition that is inducing diplopia. Current Rx is a 5^bo OU (otherwise plano OU) but this px was more comfortable wearing freznal 2^bo OD and a whopping 15^bo OS on top of the current specs.

Ideally we would like 14.5^bo OU but there is no lab willing to grind lenses, we've picked a frame with some seriously fat eye wire, frame pd is 47-18, longest diagonal is at 48 and Px pd is 57 (tiny pd doesn't help at all =( )

We have looked into a Shamir 1.67 smart lens that might be able to be cut out into 10^ OU, or Direct optical do a 1.8 glass lens in 65mm blanks but we don't know if they will be able to grind prism of this magnitude into the frame.

Also, would the fact that the lenses are plano mean that shifting the px's pd wouldn't make too much of a difference?

All this prism is a little overwhelming to be completely honest hehe

Any advice/opinions? For sake of argument, money will not be an issue to the px. (He actually said money wasn't an issue, one specialist suggested having one eye removed. No second eye, no diplopia - problem solved? :hammer: )

Very much appreciated,
Retrorat

[Darryl Meister]

this px was more comfortable wearing freznal 2^bo OD and a whopping 15^bo OS on top of the current specs... Ideally we would like 14.5^bo OU

Keep in mind that if the patient is more comfortable with most of the prism before the left eye, splitting the prism evenly between both eyes may be less effective. This is common in cases of nonconcomitant strabismus. I would certainly verify this before fabricating the actual lenses.

Also, given that the patient was comfortable with a total of 17^bo, or 2^bo + 15^bo, I assume that you are attempting to get a total 14.5^bo, and not a total of 29^bo? The use of "OU" here is ambiguous.

but there is no lab willing to grind lenses

This seems surprising to me, unless you are indeed trying to get 29^bo, total. With a 47 mm eyesize, 14.5^bo total should not be impossible to achieve with modern surfacing equippment, if you are able to split some of it between both eyes, anyway.

If you do use a high-index material, however, I would definitely recommend using a material with a high Abbe value with this much prism in order to minimize lateral chromatic aberration. 1.60 MR-8, with an Abbe value of over 40, is a good option, for instance.

tiny pd doesn't help at all... Also, would the fact that the lenses are plano mean that shifting the px's pd wouldn't make too much of a difference?

Fortunately, if the prescription is indeed close to plano, the wearer's PD shouldn't matter much at all. The edge thickness will only depend upon the prescribed prism.

one specialist suggested having one eye removed. No second eye, no diplopia - problem solved

Before cutting eyeballs out, I would try breaking the impetus to binocular fusion by blurring one eye with plus power or frosting or something. You might be able to induce suppression artificially. I suspect that this could even be achieved with a single, high-plus contact lens.

Best regards,
Darryl

[RetroRat]

Ah, sorry - that was ambiguous. What I meant by OU was the amount of prism in each eye. Ideally we would have liked 14.5^bo in each eye.

The freznal prisms were put on glasses that were already 10^bo OU (5^bo each eye - sorry) so our px is already wearing a combined 7^bo OD, 20^bo OS. This is also why we wanted to split prism equally between both eyes if we were going to consider 29^bo.

We hadn't even considered other ways of inducing suppression, thank you for that as well!

Thanks for the reply,
Retrorat

[cleyes]

If he can tolerate suppression, high plus silicone hydrogel or daily replacement SCL would be best cosmetically, also, using patch when cl not in place.
Do a one day trial wearing CL.

[Darryl Meister]

Also, before you give up on the spectacle lens route, you might talk to Michael Walach over at Quest Optical Lab. He specializes in this kind of lab work and has probably forgotten more about fabricating this kind of stuff than most people will ever know.

Best regards,
Darryl

[Jacqui]

Any competent lab should be able to make this for you, the problem is why. I would first suggest a second opinion from a qualified Ophthalmologist. I think there may be more here than you are being told.

[Darryl Meister]

Jacqui's suggestion to get a second opinion is certainly a sensible recommendation.

Also, I meant to bring this up earlier, but if you do ultimately decide to fill this prescription as spectacle lenses, I'd ask the lab about surfacing a myodisc-like carrier curve. This will significantly improve edge thickness. You might very well end up with a "lip" anyway, since the edge thickness of that much prism (around 15 mm) will probably exceed the thickness of many semi-finished lens blanks.

Best regards,
Darryl

[WFruit]

Quest Optical or Slabs Plus, both in Florida, should be able to do it for you.

I'd have to run the numbers through our system, but I think we could even do it (and they wonder why I'm pushing for a better generator). I would definitely stick to 1.60.

[Jacqui]

I could do it too, and I'm sure others could. I have to disagree with the suggestion about 1.60. Use CR-39, this much prism may induce chromatic abberation and you need all the help you can get.

[RetroRat]

Thanks all for the suggestions, only problem is I'm in Brisbane, Australia (shipping and handling is excessive, no matter how good our dollar is doing against yours :P ! )

We are currently waiting on a second specialists opinion on the matter re: suppression and from there, well we'll have to see then.

Thank you all again for your input, I'll keep you posted on what the Opthal says and which direction we head in then.

Retrorat

[RetroRat]

Okay well we had a curve ball thrown into the mix, our Px wanted his specs to be photocromic as well, we opted for a 1.53 (That's for the suggestions about chromatic abberation- thank you) through essilor and they could grind 12^bo OS and 12^bo OD with transitions. Actually, at the thickest part of the lens, it was only 11mm (roughly the same thickness of his 10^bo OU) so our px was happy.

We're ordering a 5^ freznal for the left lens which might have to be our *ahem* permanent solution as the 24^bo ou isn't enough to correct the diplopia 100% (not as good as the combined 29^)

Thank you all for the input!