which designs are optimized for low power?

[chuckles]

For a patient who has had cataract surgery and wants glasses with only a small correction for distance, plus reading/intermediate vision of course, what would be the best choice of progressive lens?

I know different lens designs optimize different things, e.g. Definity has wider intermediate zone while Physio has better side sharpness, but I don't know if these optimizations work equally well for near-plano prescriptions with add around 2.50.

Also I am assuming that you would recommend CR-39 rather than poly in this case? (Normal frames, no drilling.)

Many thanks,

[xiaowei]

For a patient who has had cataract surgery and wants glasses with only a small correction for distance, plus reading/intermediate vision of course, what would be the best choice of progressive lens?

I know different lens designs optimize different things, e.g. Definity has wider intermediate zone while Physio has better side sharpness, but I don't know if these optimizations work equally well for near-plano prescriptions with add around 2.50.

Also I am assuming that you would recommend CR-39 rather than poly in this case? (Normal frames, no drilling.)

Many thanks,

I was always wondering how applicable the results of Sheedy or any other study really are over a large range of base power, cylinder and add, not to mention inset etc. IIRC Sheedy actually used no distance power lenses
for their rating, however, depending on the coarseness of the "base curve system" the respective manufacturer uses, a non zero distance and/or stigmatic lenses might have quite different characteristics than the "zero power" one, also small changes to the prescription might change a lot in the outcome when you end up in a different "base power group". I know the manufacturers of the most advanced "free form designs" claim to use a semi-continous range of designs, but even those tell that different optimizations are done if it is high plus, a high minus, a high cylinder etcetc. case.

IMHO this also qualifies the real usefulnes of "trial sets" that some posters on this board mention (If I understood correctly a zero power trial set of the respective add to be put over the single vision glasses to demonstrate or even evaluate the relative benefits of different designs, BTW how do you adjust the exact pupil fitting?)

With respect to poly, I would assume as long as the overal power/add is low, there should be no difference here. From a theoretical-optical point of view, I cannot understand claims that poly has more "fishbowl" distortions as other material, as the overall index and not the dispersion should be relevant for that effect of the design. Maybe, one reason for this bad reputation of poly is that it is often used for special impact etc. resistant glasses that actually use different base curves to further improve mechanical stability of the lenses.

Just my 2 cents

XW

[chuckles]

I didn't read carefully enough to realize that Sheedy used zero power for distance. That is very useful to know, thanks!

However, those ratings are already out of date since they don't include newer "digital" designs like Definity and Physio/360, which is what I was considering.

As for poly vs plastic, I was not thinking of distortion (I agree that there should be no difference) but only chromatic aberration.

[Robert Martellaro]

Welcome to OB.

Some PAL designs use free-form technology, placing the reading power on the back of the lens, some also minimize skew distortion. Optimizing for position of wear should not be necessary if the lens fits close to the eyes. The inset can also be optimized for power and PD, although the standard 1.5mm to 2mm should be fine for this Rx.

What's left is choosing a lens that has a design bias towards the near, far, intermediate vision, or balanced for general use. For instance, if the eyeglasses are used primarily for near only, I would consider a short corridor design, something from the Piccolo, XS, and Ellipse family of lenses, and strongly consider STs and SV readers in addition to, or instead of PALs, especially for avid readers.

Hard to comment much further without seeing the full Rx, ophthalmic history, and details concerning your client's visual priorities. That's best left in your hands anyways, but if you get stumped on the functionality of a certain lens design, just holler.

[MarcE]

However, those ratings are already out of date since they don't include newer "digital" designs like Definity and Physio/360, which is what I was considering.

As for poly vs plastic, I was not thinking of distortion (I agree that there should be no difference) but only chromatic aberration.

In general, the "digital" designs reap more benefits for high sphere and/or high cyl. If you have neither, then you may be setting yourself up for someone who is not happy with the promises that were made.

However, there are obvious benefits from placing the add on the back side of the lens, especially for high adds in hyperopes. Again, if the person is not a strong hyperope, they the benefits of a "digital" are greatly reduced.

Also the difference in chromatic abberation between poly and CR will not be noticable inside the range of +- 2.5D. And for most people the chromatic abberation in poly is not noticeable even up to +- 4D.

All this information (like everthing I say that is remotely intelligent) was distilled from all the stuff I read on Optiboard.

[chuckles]

Also the difference in chromatic abberation between poly and CR will not be noticable inside the range of +- 2.5D. And for most people the chromatic abberation in poly is not noticeable even up to +- 4D.

I never thought of it, but of course this makes complete sense.

In general, the "digital" designs reap more benefits for high sphere and/or high cyl. If you have neither, then you may be setting yourself up for someone who is not happy with the promises that were made.

I wonder if there are 'scientific' measurements. Sheedy does not cover that.

It seems to me that making the transition from distance to near is always hard, even if the distance is plano, and a fully free-form computerized manufacturing process would be better than old-fashioned fabrication methods. But then I don't know anything about making lenses.

[HarryChiling]

What's left is choosing a lens that has a design bias towards the near, far, intermediate vision, or balanced for general use. For instance, if the eyeglasses are used primarily for near only, I would consider a short corridor design, something from the Piccolo, XS, and Ellipse family of lenses, and strongly consider STs and SV readers in addition to, or instead of PALs, especially for avid readers.

Excellent advice, I think the most important thing gleened by me from the Sheedy study was the fact that he placed impotance on teh visual tasks coupled with the designs strengths. If you notice the report is broken into near/intermediate and that is also broken into with astigmatism and without astigmatism as a factor in the ratings. I think he had a great idea for a comparison and it's the most relevent that we have available.

However, those ratings are already out of date since they don't include newer "digital" designs like Definity and Physio/360, which is what I was considering.

What does that say about our industry?

I know different lens designs optimize different things, e.g. Definity has wider intermediate zone while Physio has better side sharpness, but I don't know if these optimizations work equally well for near-plano prescriptions with add around 2.50.

Near plano high add, I find that these patients will not do well in lenses that have compirmised distance viewing zones. My personal choice for fit would be a lens with a uncomprimised distance and a optmized near, for get the intermediate if they need something for this they will need another pair. Here is my line of thought. Whenever I have placed a near plano wearer in comprimised distance they rarely focus on the improved near or intermediate they almost always focus on the degraded distance. The most common complaint is, "I can see better with my glasses off". So fro me the focus tends to be on a wide clear distance zone and a wide near zone. With that said hard designs all the way for this type of patient. Hard desings also tend to be tougher to get used to especially for first time wearers I find as the corridor tends to get lost and the sharp increase in astigmatism in the periphery of the corridor makes this area unusable, but patient satisfaction will also be greater in this design at least from our offices standpoint (anecdotal evidence). Anyway gender plays a role and the personality also plays a role. You'll find that your prep with these patients before fit will be the most imperative piece the better you prepare them the better the possibility of a successful fit.

I think this document here will give you some really great info related to your question, I find it invaluable and am suprised that more people don't read it. Attachment 1838

[john-atlanta]

In this case I disagree a bit with Harry, but it really depends upon usage.

The key is NOT that they are plano, but rather, do they wear the glasses for television and driving or primarily just for office tasks. In a case like this, I prefer a non digital design that is more of a hybrid, namely the new Piccolo and the Creation ("freeform optics"). Which lens? depends on what tasks the patient wears them for and more importantly when the patient doesn't wear them.

It is also important to remember that prior to cat sx, this patient had compromised vision and was likely NOT plano, so they will be easier to please with a short corridor than the patient described by Harry.


John

[HarryChiling]

It is also important to remember that prior to cat sx, this patient had compromised vision and was likely NOT plano, so they will be easier to please with a short corridor than the patient described by Harry.

I missed the cat sx, must have not registered.:hammer:I would probably still go the same way, but they would more than likely be an easier fit than my description since their vision is more than likely vibrant now compared to what it was, hopefully you catch them on that cat sx high they get for the first few months after sx. Also the shorter orridors tend to be more often than not hard designs so we actually agree without agreeing. :cheers: awesome.

[au]

Hi XW,

IMHO this also qualifies the real usefulnes of "trial sets" that some posters on this board mention (If I understood correctly a zero power trial set of the respective add to be put over the single vision glasses to demonstrate or even evaluate the relative benefits of different designs, BTW how do you adjust the exact pupil fitting?)

The trial lens set have an adjustable pd and pantoscopic tilp for pt. The PD is from 54 to 70mm and P.T. have 3 choice. However the BC of the frame is flat, no curve. In some case of high myope, because using lens + lens, some feel less different han normal. In most of the case, we tell the pt have 70% accuracy, they are OK and acceptable.

BTW it is the best way to show pt how they feel instead of telling than what will happen because we may have different judgement on feelings. It works good for me.
:cheers:

[HarryChiling]

Hi XW,


The trial lens set have an adjustable pd and pantoscopic tilp for pt. The PD is from 54 to 70mm and P.T. have 3 choice. However the BC of the frame is flat, no curve. In some case of high myope, because using lens + lens, some feel less different han normal. In most of the case, we tell the pt have 70% accuracy, they are OK and acceptable.

BTW it is the best way to show pt how they feel instead of telling than what will happen because we may have different judgement on feelings. It works good for me.
:cheers:

I think what he may mean with the trial lenses is that they are made in an equi-convex or equi-concave form, the lenses are made that way because it's much easier to have a doctor place a lens in the trial frame in a dark exam room without having to remember which side has the correct back vertex power. This creates an issue with off axis viewing through any of these trial lenses as the form is not meant to accomplish off axis viewing so when you put a trial lens in the frame that has a varifocal lens in it and the patient views off axis the trial lens is going to introduce error.

[au]

Thanks Harry, that's correct. Just remember to tell them 70% accucacy !
:D

[HarryChiling]

Thanks Harry, that's correct. Just remember to tell them 70% accucacy !
:D

Will do. ;)