question about plano lenses with prism

[Song]

Hi everyone, I am filling a Rx which is Plano lenses with 3.00 Base In Prism on both eyes. I got the lenses from my surfacing lab and cut them in the frame with the thicker sides on the nasal side. On the lensometer it shows Base In on both lenses and everything looks fine. However the patient was not happy with them and I am afraid that I had make a mistake to have done it on a wrong way? My question is, with this Plano Rx 3.00 Base In Prism, is it correct that the nasal sides of the lenses is thicker than the temple sides? Did I do it wrong?

Many thanks for helping me!

[gmc]

You did it right. May be an adaptation issue, particularly if there was a change in prism.

[Song]

thank gmc! I think so too.

[gmc]

There is another possibility. Is the Rx written as 3.0 BI OU meaning 6 diopters total or for three diopters total? Miscommunication sometimes happens.

[Song]

The Rx should be 3.0 BI for each eye.

[Song]

any more comments? Thanks

[Speed]

any more comments? Thanks

Did the thickness look OK? Thin enough on the thin side or too thick?

[MikeAurelius]

Somebody probably told the patient they look awful wearing them causing buyer's remorse. Might be time for a sit-down with the patient and explain that they can wear the glasses and have corrected vision and be able to drive and walk around, or not wear the glasses and not be able to see or drive or walk around safely.

[Turd Ferguson]

If the patient has not worn prism before, it would be a shock to go into a 6D imbalance. More history would help.

My experience with doctors is that prescribing prism is far from an exact science. If the patient has it in their current eyewear the doc will usually just match it. Either way, it's not unusual for it to take a try or two to get it where it works best for them. I'd start with a sit-down like MikeA describes, and advise them to see the dr again (and take the glasses you made with them) to possibly fine tune things. Also, Speed has a good point about thickness. It's not hard to block the lenses so even the thinnest part of the lens is too thick, making the patient look through too much material unnecessarily.

[Craig]

I tell folks as soon as they put them on they know if the RX is correct or not.
If you made them correctly and the Pd's are accurate it is an RX issue.
Hard to imagine a plano with all that prism; we have never seen anything like that for regular glasses.

[MakeOptics]

Dot them in your lensometer at 3PD BI and check the PD for accuracy, you may find that the PD's are off, you need to compensate lenses with that much prism when blocking. 1mm for every 3PD in this case you are probably 2mm off.

[drk]

I don't think there would be a pd in this case.

It's 3^ everywhere in the lens.

[AngeHamm]

I don't think there would be a pd in this case.

It's 3^ everywhere in the lens.

That would be true if it was vertical prism, but not with horizontal.

[Robert Martellaro]

Hi everyone, I am filling a Rx which is Plano lenses with 3.00 Base In Prism on both eyes. I got the lenses from my surfacing lab and cut them in the frame with the thicker sides on the nasal side. On the lensometer it shows Base In on both lenses and everything looks fine. However the patient was not happy with them and I am afraid that I had make a mistake to have done it on a wrong way? My question is, with this Plano Rx 3.00 Base In Prism, is it correct that the nasal sides of the lenses is thicker than the temple sides? Did I do it wrong?

Many thanks for helping me!

I assume that you know that you have to be more accurate than placing "the thicker sides on the nasal side". Check for VI!

https://c.ymcdn.com/sites/www.covd.o...enses_Pris.pdf

Scroll down to Prism Image Formation. Expect adaptation times of about two weeks.

I don't think there would be a pd in this case.

It's 3^ everywhere in the lens.

There's an IPD, but the OC may not exist (and doesn't in this case). In this example, the OC is moot because all we care about is the PRP (acronym hell).

[MakeOptics]

I don't think there would be a pd in this case.

It's 3^ everywhere in the lens.

From a purely mechanical perspective, the lenses were mounter with aN auto bevel setting, if this means a 40/60 or 50/50 the lenses are mounted at a slight tilt. The normal to the front surface is going to be off by this degree so the exiting ray will be off as well. Since the lenses are already made up the simple solution is to check the prIsm at the pd or pd at the prism. Optically with zero power the lenses ideally would be 3PD all the way through, realistically the prism formula is just an approximation so we know it does not hold true especially in low powers, to take for into account is not a trivial exercise and since the lenses are made up check the prism at the pd or pd at the prism.

[mshimp]

I don't think there would be a pd in this case.

It's 3^ everywhere in the lens.

+1. That's certainly not the problem.

[drk]

Hmm. Good info.

I know that when lens wrap calculations are done for power lenses, we have a prism induction.

So, why not a little face-form prism compensation for a prism?

Seems logical.

(Nevertheless in this case it's not likely to be germane.)

[drk]

I tell folks as soon as they put them on they know if the RX is correct or not.

Hey, Snook-fishin-optishin, do you really tell them that? Don't you believe in adaptation?

[Paul Smith LDO]

Hi everyone, I am filling a Rx which is Plano lenses with 3.00 Base In Prism on both eyes. I got the lenses from my surfacing lab and cut them in the frame with the thicker sides on the nasal side. On the lensometer it shows Base In on both lenses and everything looks fine. However the patient was not happy with them and I am afraid that I had make a mistake to have done it on a wrong way? My question is, with this Plano Rx 3.00 Base In Prism, is it correct that the nasal sides of the lenses is thicker than the temple sides? Did I do it wrong?

Many thanks for helping me!

What material choice was made for the patient. Is this their first rodeo with prism, if so, it would not be unusual for someone to require a period of adaptation. If they have had prism before, how much.

[Don Gilman]

The prism could appear to be the same ie. thicker on the nasal side, but if one is twisted a little up and the other a little down unknown amount of vertical prism would be induced. Om the table of a lensometer they should both on the same plane on the 180.

[Tallboy]

I always use the Shamir Spectrum SV for Prism now (plano included), a great solution.

Clarity should be immediate from a New RX if its correct, but depth perception shifts and a feeling of Vertigo can be common, adaptation to those things is a fact of dispensing glasses

[mshimp]

I hope poly wasn't used with that much prism?!

[icmor]

I don't see any mention of A/R coating on the lenses. Was A/R used? It definitely should be on there if it's plano lenses.