atoric/aspheric

[mirage2k2]

Read an interesting article on atoric lenses - http://www.visioncareproducts.com/19/lens_atoric.html
Anyone know much about them/dealt with them? Article suggests that aspheric lenses are less suitable for Rx with high cylinder.

I'm assuming that atoric, atoric/aspheric and bi-aspheric are all the same thing - right?

[William Stacy O.D.]

Read an interesting article on atoric lenses - http://www.visioncareproducts.com/19/lens_atoric.html
Anyone know much about them/dealt with them? Article suggests that aspheric lenses are less suitable for Rx with high cylinder.

I'm assuming that atoric, atoric/aspheric and bi-aspheric are all the same thing - right?

I've never used them, and I don't even know if I've ever seen one (how would I know?) It's all nice theory for higher power lenses, esp. progressives in higher powers, but I don't think it's caught on very well. Somebody correct me esp. if they have any statistics on the numbers actually being manufacturere/dispensed...

[David Wilson]

Darryl has written an excellent article on atorics. You'll find it in the OptiBoard files. Essentially, an aspheric surface is used to reduce the effects of aberrations, notable oblique astigmatism, which are created by using a flatter lens form. However, if the script has a high cyl then the asphericity used cannot be ideal for both power meridians. An atoric lens has different asphericity in both of its principal meridians, thereby having the ideal asphericity for both.

Regards
David

[mirage2k2]

You have said "an aspheric surface is used to reduce the effects of aberrations, notable oblique astigmatism, which are created by using a flatter lens form" ... would you say they are comparible to a best form lense that uses a good base curve, or put differently, would you say the abberations created by the flatter lens form are sufficiently reduced by the aspheric surface?

If the asphericity in a standard aspheric is only ideal for one power meridian what about the other? The flatter lens form is creating abberations in two power meridians and then only correcting one - right? So I suppose what I'm getting at is - for a person with high cyl Rx, is it possible that their vision might be better in a best form lense because they pick up the uncorrected abberations in the aspheric lense?

[drk]

The bottom line is that with spherocylinders, one meridian (the more minus) will oftentimes not be optimized with spherical or aspheric design, as the base curve has to be chosen for one meridian, only. With atoric design, this problem is minimized.

I'm not sure, but I don't believe it's more detrimental to have an aspheric design with high cylinder than a spherical design with high cylinder. An atoric design, though, would trump both.

[mirage2k2]

I'm guessing that the difference here though, is that the aspheric lense, thanks to its flatter base curve, has generated lots of abberations in both meridians, and then only corrected those abberations in one - right?. It might be possible that the cyl abberations in a best form lense are not as bad as the generated (and then uncorrected) cyl abberations in the aspheric?

I'm supposing, with my limited understanding of these things, it would be very similar to comparing two spherical lenses, one with a flat base curve, and one with a steep base curve, both of which are optimized for the sphere. Since neither are optimized for the cyl, which one would have less cyl abberations?

[drk]

I know what you mean, there, but I do not have the answer.

[lensgrinder]

You have said "an aspheric surface is used to reduce the effects of aberrations, notable oblique astigmatism, which are created by using a flatter lens form" ... would you say they are comparible to a best form lense that uses a good base curve, or put differently, would you say the abberations created by the flatter lens form are sufficiently reduced by the aspheric surface?

Using an aspheric lens form helps reduce the overall thickness and weight of the lens, the off-axis optics of ashperics are close to the same as a best form lenses. Best form lenses are not optomized for clinder either. So, ashperics are comparable to best form lenses in optics only, best form lenses give you a thicker and heavier lens.

I'm supposing, with my limited understanding of these things, it would be very similar to comparing two spherical lenses, one with a flat base curve, and one with a steep base curve, both of which are optimized for the sphere. Since neither are optimized for the cyl, which one would have less cyl abberations?

That would depend on the powers of the lens in their principle meridians. I would suggest you read Darryl and Mo Jalie's article on aspherics. Jalie's article is found here

http://www.optometry.co.uk/pages/art...iclesearch.php

Hope this helps

[AWTECH]

Aspheric, Best Form Lens, etc. Don't we need some control of these terms since they no longer mean what they did when originally used.

A Best Form Lens does not necessary give the patient the best optical view available to him or her. With individualized non-spherical (I did not use the term aspheric since it has morphed itself in the optical prescription world to mean a design using a non spherical curve that reduces as oblique astigmatism in one meridian), single vision lens designed with the help of ray tracing software will allow the patient to see better than with a Best Form Lens.

The words "Best Form Lens" implies The Best Form which with todays technology it is not.

Imagine the patient hearing two years ago that they were fitted with a Best Form Lens, and now they are being fitted with a non-spherical ray tracing designed freeform custom lens. The patient asks shouldn't I have the Best Form Lens and now you have to try to explain how Best does not mean Best.

Aspheric to the rest of the world means: NON-SPHERICAL (it has nothing to do with lens design.)

An Atoric lens is thought to be a more advanced lens than an aspheric lens.

Well the fact is to the rest of the world an Atoric lens is: Aspherical (because it is non spherical)

Just some food for thought: Comments anyone?

[HarryChiling]

To help simplify things lets use this example:

power -1.75 -3.00 x 050

the power in the 050 meridian is -1.75
and the power in the 140 meridian is -4.75

if we were to select the base curve for this lens we would take the spherical equiv. divide by 2 then add 6.

base= -3.25/2 + 6
base= -1.625 + 6
base= 4.375

lets say that we wanted to optimize the base for both meridians. Then we would not use the spherical equiv., but the actual powers at both meridians:

base@050= -1.75/2 + 6
base@050= -0.875 + 6
base@050= 5.125

base@140= -4.75/2 + 6
base@140= -2.375 + 6
base@140= 3.625

This would give us a lens that has the most optimal base curve for both power meridians acording to Vogels Formula. Atorics use the same principal except they are not giving you the optimal base curve, but rather the best aspheric coefficient that would correct lens abberations (eg saggital and tangential error, risidual astigmatism, and coma). If you were to take Darryls Optical Analysis program and play around with it you will see kinda how this works.

for the same rx if you were to look at the difference in Mean Power Error (MPE) at a eye rotation of 49.5 degrees or a ray height of about 25mm off center in a hard resin lens (n=1.498)

a lens with best base curve acording to vegels formula using spherical front surface:

base@050 and 140=4.375
MPE@050=-0.23
MPE@140=+0.55
Difference=0.78

A lens with the base optimized at both meridians surfacing both front and back according to vogels formula

base@050=5.125
base@140=3.625
MPE@050=-0.30
MPE@140=+0.45
Difference=0.75

A lens with Best Base curve acording to vogels formula and optimized aspherics in both meridians

base@050 and 140=4.375
p@050=1.2
p@140=-1.8
MPE@050=+0.02
MPE@140=+0.03
Difference=0.01

You can see that in the example above the atoric lens cuts the Mean Power Error by almost 0.75 Diopters which is alot. This is using a lower Rx, imagine what it can do for your high Rx's or Rx's with very high cyl. I personaly work in a pediatric ophthalmology practice it is not uncommon for me to see powers in excess of 9 Diopters about once or twice a week and cyls in excess of 5 diopters about once a week. This is a welcome technology.

[Ray Parent]

Just a personal observation/experience. I wore the Vizio for about 3 years and after having a second pair made up in an identical fashion (tma, same size, shape and rx) but with Essilor's 1.67. I definitely was far more comfortable with the Vizio.

rx is -6.50 -1.50 x140
-3.75 -1.25 x32

It might just be in my head, but after wearing the Essilor 1.67 for about 6 months now with a more current rx, I am tempted to try the Vizio's again.

[drk]

To help simplify things lets use this example:

power -1.75 -3.00 x 050

the power in the 050 meridian is -1.75
and the power in the 140 meridian is -4.75

if we were to select the base curve for this lens we would take the spherical equiv. divide by 2 then add 6.

base= -3.25/2 + 6
base= -1.625 + 6
base= 4.375

lets say that we wanted to optimize the base for both meridians. Then we would not use the spherical equiv., but the actual powers at both meridians:

base@050= -1.75/2 + 6
base@050= -0.875 + 6
base@050= 5.125

base@140= -4.75/2 + 6
base@140= -2.375 + 6
base@140= 3.625

This would give us a lens that has the most optimal base curve for both power meridians acording to Vogels Formula. Atorics use the same principal except they are not giving you the optimal base curve, but rather the best aspheric coefficient that would correct lens abberations (eg saggital and tangential error, risidual astigmatism, and coma). If you were to take Darryls Optical Analysis program and play around with it you will see kinda how this works.

for the same rx if you were to look at the difference in Mean Power Error (MPE) at a eye rotation of 49.5 degrees or a ray height of about 25mm off center in a hard resin lens (n=1.498)

a lens with best base curve acording to vegels formula using spherical front surface:

base@050 and 140=4.375
MPE@050=-0.23
MPE@140=+0.55
Difference=0.78

A lens with the base optimized at both meridians surfacing both front and back according to vogels formula

base@050=5.125
base@140=3.625
MPE@050=-0.30
MPE@140=+0.45
Difference=0.75

A lens with Best Base curve acording to vogels formula and optimized aspherics in both meridians

base@050 and 140=4.375
p@050=1.2
p@140=-1.8
MPE@050=+0.02
MPE@140=+0.03
Difference=0.01

You can see that in the example above the atoric lens cuts the Mean Power Error by almost 0.75 Diopters which is alot. This is using a lower Rx, imagine what it can do for your high Rx's or Rx's with very high cyl. I personaly work in a pediatric ophthalmology practice it is not uncommon for me to see powers in excess of 9 Diopters about once or twice a week and cyls in excess of 5 diopters about once a week. This is a welcome technology.

Nice post. What atoric do you use? Vizio? I'd doubt it. Resolution? I've heard a concern that Optima has not enough atoric base curves to choose from, for the atoric effect to work especially well, although I'm rather ignorant on the subject. Would the optical lab need to pull a blank with atoricity on the front surface optimized for -2.00DC, -2.50DC, -3.00DC? Any information on that?

[HarryChiling]

Thank you for your comment on the post I know of the Vizio lens and also the nike sunglasses apparently have atoric lenses in them if ordered through marchon. I have never worked with one before, but am familiar with the theory behind the lens design because I have surfaced both sides of a lens before to optimize base curves before. It is a similar principal for the asphericity.

[William Stacy O.D.]

...
for the same rx if you were to look at the difference in Mean Power Error (MPE) at a eye rotation of 49.5 degrees or a ray height of about 25mm off center...
You can see that in the example above the atoric lens cuts the Mean Power Error by almost 0.75 Diopters which is alot.

.75 is a fair amount, except that you are talking 50 degrees or 25 mm off axis. Who uses that part of their lens (if it exists at all in this world of less than 15 mm from the geo center to the top eyerim) for anything except peripheral vision? Most people can't even rotate their eyes that far comfortably. I think these kind of calcs should be for the regions of the lens that the eye is likely to rotate to, say 5 mm off axis. I think the reason it's not done is because the error there is pretty darn small. Nothing to get excited about.

[Robert Martellaro]

.75 is a fair amount, except that you are talking 50 degrees or 25 mm off axis. Who uses that part of their lens (if it exists at all in this world of less than 15 mm from the geo center to the top eyerim) for anything except peripheral vision? Most people can't even rotate their eyes that far comfortably. I think these kind of calcs should be for the regions of the lens that the eye is likely to rotate to, say 5 mm off axis. I think the reason it's not done is because the error there is pretty darn small. Nothing to get excited about.

Multifocal wearers are looking 10mm to 18mm off-center, where lateral chromatic aberration, oblique astigmatism, and power errors are a real concern, especially in the higher sphere and/or cylinder powers. Even when the aberrations are minor and/or when the gaze is usually central, there is a clear sense of an increase in visual refinement when looking through a lens that has been designed in a way that minimizes off-center aberrations, similar to the way an anti-reflection coated lens feels compared to an uncoated lens. This has been my personal experience, and corresponds well with feedback from my clients and other ophthalmic dispensers.

Regards,

[QDO1]

Multifocal wearers are looking 10mm to 18mm off-center

and the rest - for some of the longer corridor lenses I would say 24 - 28 mm can be useful.

I have also noted that although the periphery of any lens is hard to use, patients appreciate that part of the lens (if present) presenting a clearer image. when the optics are poor in that region, often patients complain of effects like curvature and sloaping

It ought to be noted, that the closer fitting the lens, the harder it is for the patient to see the periphery, and the less effect the periphery of the lens has on the patients vision... conversley the further away a frame fits, the more the effect of the peripheral lens, and the easiier the patient finds to rotate to use that part of the lens

[William Stacy O.D.]

and the rest - for some of the longer corridor lenses I would say 24 - 28 mm can be useful.

I have also noted that although the periphery of any lens is hard to use, patients appreciate that part of the lens (if present) presenting a clearer image. when the optics are poor in that region, often patients complain of effects like curvature and sloaping

It ought to be noted, that the closer fitting the lens, the harder it is for the patient to see the periphery, and the less effect the periphery of the lens has on the patients vision... conversley the further away a frame fits, the more the effect of the peripheral lens, and the easiier the patient finds to rotate to use that part of the lens

I agree with you guys that it should be better if designed better, but the proof to me is in the numbers. Until they start mapping out these lenses with actual cyl values at various points in the periphery, it's impossible to quantify the differences. Testamonials just don't do it for me.

[QDO1]

I agree with you guys that it should be better if designed better, but the proof to me is in the numbers. Until they start mapping out these lenses with actual cyl values at various points in the periphery, it's impossible to quantify the differences. Testamonials just don't do it for me.

its even harder than that - these lenses can be designed so the image presented at the eye is free of (or has reduced) many of the off axis abberations, for a given lens form. that might mean they achieve that by adding (for example) extra astigmatim, or a change in power at the periphery, to counteract the expected distortions, for the measured position in space for the given lens.

Rodenstock (for example) has released a free form single vision near lens with this in mind. What this means in practice is that a lens that the patient reports as amazingly clear to the periphery, could in theory, look terrible on a focimeter at the periphery

[Darryl Meister]

In lens design, 30 degrees (roughly 15 mm) is typically the angle used for optical evaluation. (It is interesting to note that the original ANSI Standard included tolerances on optical powers at 30 degrees for so-called "corrected curve" lenses.)

[William Stacy O.D.]

its even harder than that - these lenses can be designed so the image presented at the eye is free of (or has reduced) many of the off axis abberations, for a given lens form. that might mean they achieve that by adding (for example) extra astigmatim, or a change in power at the periphery, to counteract the expected distortions, for the measured position in space for the given lens.

Rodenstock (for example) has released a free form single vision near lens with this in mind. What this means in practice is that a lens that the patient reports as amazingly clear to the periphery, could in theory, look terrible on a focimeter at the periphery

I have a hard time believing that something that looks terrible in a lensometer will perform just perfectly on the face. Let me give you a simple example. Chromatic aberrations are easily seen in a lensometer as horrible distortions. And that's how they look looking through the lenses with your eyes. If they correct chroma in the lens, the lensometer image ought to be better too. I wasn't from Missouri, but my dad was...

[Darryl Meister]

The periphery of an aspheric won't look horribly distorted, but the power will measure slightly off. Consider a +4.00 DS lens on a 6.00 Base. At 15 mm from the optical center, the lens will actually measure +4.06 DS -0.05 DC in a focimeter. However, the power perceived by the actual wearer at this same point (representing an angle of view of roughly 30 degrees) will be +4.49 DS -0.48 DC. Because of the oblique astigmatism, the lens introduces an average power error of nearly +0.25 DS combined with almost 0.50 DC of unwanted cylinder power. In order to correct this error, an aspheric surface would have to change by about this much at the same point, but in the opposite direction.

[William Stacy O.D.]

The periphery of an aspheric won't look horribly distorted, but the power will measure slightly off. Consider a +4.00 DS lens on a 6.00 Base. At 15 mm from the optical center, the lens will actually measure +4.06 DS -0.05 DC in a focimeter. However, the power perceived by the actual wearer at this same point (representing an angle of view of roughly 30 degrees) will be +4.49 DS -0.48 DC. Because of the oblique astigmatism, the lens introduces an average power error of nearly +0.25 DS combined with almost 0.50 DC of unwanted cylinder power. In order to correct this error, an aspheric surface would have to change by about this much at the same point, but in the opposite direction.

I know that, because toric defocus is handled nicely by a lensometer. But you were discussing higher order aberrations, like chroma, coma, trefoil and the rest. Unless they bring out a simple clinical instrument for measuring those things on an ophthalmic lens, it'll never catch on, at least in my office, because I would be in a position of having to say "well it looks awful in the lensometer, but the manufacturer says it's supposed to look that way"!!!

[Darryl Meister]

But you were discussing higher order aberrations, like chroma, coma, trefoil and the rest.

Aspheric and atoric lens designs are generally not designed to eliminate coma and trefoil.

[William Stacy O.D.]

Aspheric and atoric lens designs are generally not designed to eliminate coma and trefoil.

OK maybe I misread the post. qdo1 had said: "What this means in practice is that a lens that the patient reports as amazingly clear to the periphery, could in theory, look terrible on a focimeter at the periphery"

I took that to mean higher order aberrations, not just sphero-cylindrical defocus, as THAT kind of defocus should look just fine in the lensometer, although it will obviously require the operator to move the power wheel (and probably also the axis wheel). I guess I was thinking about these wave front lenses that some are hyping. :hammer:

[mirage2k2]

How does the abbe value of the lens affect these things? Given that the lense contains atoric/aspheric designs to counteract abberations, you would imagine that the abbe value of the lense would make less of a difference.

You would expect that the atoric/aspheric design in a 1.74 would be different to that in a good 1.6, since the 1.74 has more abberations to deal with! Are the designs tailored to the particular lense material, or does the lense manufacturer come up with a good atoric/aspheric design and then just slap it on all lenses in a certain range, irrespective of the index/abbe value, etc?