Varilux Physio comments & feedback please

[Andrew Weiss]

First, this is one of the most educational threads I've encountered on the board in awhile (another is the Vision Source progressive thread). I'm really grateful for the presence of people like Darryl, Kyle, dbracer and others who not only have the knowledge but also the ability to explain things simply and clearly. What a gift! Thanks to you all.

And to Tim -- g'day mate, welcome aboard! My wife hails from Melbourne; we have family there and in Brisbane, Sydney and Hobart. Whereabouts are you based? And don't take things here too seriously. The attitude toward Essilor is a combination of some not-so-great experiences and more than a bit of "tall poppy" syndrome.

[dbracer]

Good post,

You're right. Coordinates drive me nuts, and there just a means to a location end.

You're right. Just like a lot of "ometers" out there, aberrometer is just a combination of syllables.

However, there is no way around analyzing the wavefront aberrations of the actual eye before attempting to correct those -- at least beyond assuming a nominal correction for spherical aberration.

But aren't you begging the question here? Why do we need to analyze the eye when the wearer of an unaltered eye has no complaints? He only has complaints with the spectacle alteration of incident light, right?

But keep in mind that a spectacle lens cannot fully eliminate the wavefront aberrations of the eye, anyway, without introducing additional lower- and higher-order aberrations as the eye rotates behind the lens.

Here again the unaltered eye has no aberrations of human concern until the spectacles alter incidence, right?

The industry has done a pretty good job of dramatically improving the PA distortion and disorientation from those of the old AO progressive first introduce in the 70's.

So I would think that using wave front analysis could further improve the industry.

Respectfully,
dbracer

[dbracer]

First, this is one of the most educational threads I've encountered on the board in awhile (another is the Vision Source progressive thread). I'm really grateful for the presence of people like Darryl, Kyle, dbracer and others who not only have the knowledge but also the ability to explain things simply and clearly. What a gift! Thanks to you all.

And to Tim -- g'day mate, welcome aboard! My wife hails from Melbourne; we have family there and in Brisbane, Sydney and Hobart. Whereabouts are you based? And don't take things here too seriously. The attitude toward Essilor is a combination of some not-so-great experiences and more than a bit of "tall poppy" syndrome.

Your are definitely overrating me, and putting me in a class of my superiors, but I'll take the compliment anyway.

Respectfully,
dbracer

[Darryl Meister]

But aren't you begging the question here? Why do we need to analyze the eye when the wearer of an unaltered eye has no complaints?

But I'm not suggesting that we do need to measure them. I'm simply saying that the aberrations produced by the spectacle lens are independent of the aberrations produced by the eye, though they will obviously interact to some degree, and that if you want to minimize the aberrations of the eye, you need to know what they are, first (using a wavefront sensor, for instance).

Here again the unaltered eye has no aberrations of human concern until the spectacles alter incidence, right?

This quote was originally referring to lenses that have attempted to minimize any higher-order wavefront aberrations of "human" concern. The spectacle lens can correct those aberrations only for a single angle of view. As for whether or not those higher-order ocular aberrations should've been corrected in the first place, I guess it would really depend upon the individual wearer. Though, in general, I think you are much better off getting a carefully determined second-order correction that considers the "effects" of the higher-order aberrations on lower-order sphere and cylinder errors and maximizing the depth of focus of the eye over a wide range of luminance levels.

The industry has done a pretty good job of dramatically improving the PA distortion and disorientation from those of the old AO progressive first introduce in the 70's.

Yes, indeed. And those aberrations are considerably more detrimental to vision than the higher-order aberrations (of either the spectacle lens or the eye).

So I would think that using wave front analysis could further improve the industry

You may have lost me here; I thought you were arguing against the necessity of measuring and correcting higher-order wavefront aberrations...?

[drk]

Summary:
Physio: lens' higher order aberrations.
I-zon: eye's higher order aberrations (claim).
Custom ablation: ablation pattern's higher order aberrations.

Now, the nagging residual questions:
1.) Definity only puts +0.75 on the back? That's not that big a deal. I'm suprised.

2.) Is there higher-order lens aberration control in other designs?

3.) How much bang does an internal progressive provide? Yeah, the keyhole effect, and all, but maybe 2mm in a low minus lens matters. I guess I can understand that 5mm in a thick minus lens matters.

How about that, low power thin lenses vs. high power thick lenses and the variable keyhole effect?

4.) How to conceptualize the optical advantage of two-sided digital surfacing in the distance portion? How is 5 + 5 better than 10 + 0 ?

[dbracer]

You may have lost me here; I thought you were arguing against the necessity of measuring and correcting higher-order wavefront aberrations...?

lol, Darryl. We're now becoming a comedy of errors, mainly because of my poor communication skills.

No, I'm actually supporting consideration of higher order aberrations in PA's, or high &/or unusual powers to provide more optically compatible and acceptable lenses.

The intra-ocular higher order aberrations aren't part of this picture, because the average human wearer of unaltered healthy eyes has no problem with them. The higher order aberrations caused by the correcting lenses is what disorients the patient.

In that same line of reasoning, I think some of the refractive surgery technology just might be helpful in producing better PA's, and other complex lenses.

What do you think, Darryl?

Respectfully,

[dbracer]

Summary:
Physio: lens' higher order aberrations.
I-zon: eye's higher order aberrations (claim).
Custom ablation: ablation pattern's higher order aberrations.

Now, the nagging residual questions:
1.) Definity only puts +0.75 on the back? That's not that big a deal. I'm suprised.

2.) Is there higher-order lens aberration control in other designs?

3.) How much bang does an internal progressive provide? Yeah, the keyhole effect, and all, but maybe 2mm in a low minus lens matters. I guess I can understand that 5mm in a thick minus lens matters.

How about that, low power thin lenses vs. high power thick lenses and the variable keyhole effect?

4.) How to conceptualize the optical advantage of two-sided digital surfacing in the distance portion? How is 5 + 5 better than 10 + 0 ?

Hey drk,

I think you may have some pretty good questions here. I just don't quite understand them -- not that I have the answers.

Could you expound a little?

Respectfully,
dbracer

[Darryl Meister]

The intra-ocular higher order aberrations aren't part of this picture, because the average human wearer of unaltered healthy eyes has no problem with them. The higher order aberrations caused by the correcting lenses is what disorients the patient.

As it turns out, the higher-order aberrations produced by modern progressive lenses are seldom greater in magnitude than the higher-order aberrations of the wearer's own eyes (see, for instance, Villegas et al., "Spatially Resolved Wavefront Aberrations of Ophthalmic Progressive-Power Lenses in Normal Viewing Conditions" Optom. Vis. Sci. Vol. 80, No. 2). Secondly, lower-order astigmatism and defocus dominate most of the progressive lens surface. One could conceivably argue that small amounts of higher-order aberrations may increase the wearer's depth of focus and, consequently, improve the wearer's tolerance to the blur by the second-order aberrations of the progressive lens.

In that same line of reasoning, I think some of the refractive surgery technology just might be helpful in producing better PA's, and other complex lenses

I'd hate to see wavefront correction referred to as "refractive surgery technology," simply because this technology was around long before refractive surgeons ever started using it. Also, while the goal of wavefront-guided ablation is often to achieve supernormal visual acuity by correcting higher-order aberrations, this goal is seldom realized. While wavefront-guided ablation certainly minimizes the wavefront aberrations traditionally produced by the refractive surgery, itself, such as spherical aberration, clinical studies have demonstrated that postoperative results are frequently no better than the patient's best corrected acuity prior to surgery.

Now, the nagging residual questions

Hasn't this Physio thread been derailed enough? ;)

2.) Is there higher-order lens aberration control in other designs?

Some lens designs result in inherently low levels of higher-order aberrations because of specific choices made by the lens designers, such as minimizing the gradients -- or rates of change -- in power and astigmatism. Certainly, the presence of higher-order aberrations in a progressive lens surface as a result of rapid changes in power have been long understood. I have a 25-year-old book from Mo Jalie that discusses these optical principles in detail.

3.) How much bang does an internal progressive provide?... How to conceptualize the optical advantage of two-sided digital surfacing in the distance portion? How is 5 + 5 better than 10 + 0 ?

In terms of astigmatism and blur, the differences are negligible between front versus back versus dual surface designs, since 5 + 5 does indeed equal 10 + 0 (at least for thin-ish spectacle lenses).

Still, one could argue that moving the optics to the back surface 1) Brings the limiting apertures closer to the eye thereby slightly increasing the fields of view, 2) Reduces distortion since differences in front surface curvature contribute to magnification effects, and 3) Minimizes the potential for surface alignment errors. Lastly, if you believe that free-form surfacing produces a more accurate lens surface, one could also argue that it is better to free-form surface the progressive lens design, not just the optimized prescription curves.

[drk]

You are most kind, and most wise, Darryl-san.

Your dilligent responses fill the oceans

with deep waters of understanding..:D

[Pete Hanlin]

Physio: lens' higher order aberrations.
I-zon: eye's higher order aberrations (claim).

Concisely put... The visual system of an ametrope consists of both the eye itself plus any corrective lens placed in front of the eye. Therefore, higher order aberrations in either the eye OR the corrective lens will increase the higher order aberrations of the system (and decrease the modulation transfer function of the system- which results in a lower contrast sensitivity threshold).

Ophthonix has a system that measures higher order aberrations in the eye, then attempts to resolve those aberrations with the corrective lens. Varilux Physio, Varilux Physio 360, and Varilux Ipseo reduce the higher order aberrations in the corrective lens, but do nothing to correct higher order aberrations in the eye itself. The progression of Varilux Physio & Varilux Physio 360 is placed entirely on the front of the lens- the progression of Varilux Ipseo is placed on the back (along with the distance power).

As Darryl notes, some PALs inherently have less higher order aberration than others- simply as a result of other design characteristics. W.A.V.E. Technology is a design characteristic specifically focused on lowering higher order aberrations. As a result, lenses with WAVE Technology have little or no higher order aberration in the area of the lens primarily used for distance viewing.

Definity only puts +0.75 on the back? That's not that big a deal. I'm suprised.
Well, J&J thought it was a big deal when they launched DEFINITY, and Essilor must have thought it a big enough deal when they subsequently purchased the technology. The primary feature of DEFINITY is low levels of unwanted astigmatism. Typically, you can change a PAL wearer from a +1.50 ADD in a traditional (front surface only) PAL, change them to a DEFINITY, and- even if the ADD power in the new lenses is +2.00- the level of unwanted astigmatism will decrease in the new DEFINTY lenses.

Best regards,
Pete

[Darryl Meister]

Ophthonix has a system that measures higher order aberrations in the eye, then attempts to resolve those aberrations with the corrective lens.

I agree that they are measuring the higher-order aberrations of the eye with their aberrometer, though I would argue that it is mathematically impossible to correct those aberrations fully with a spectacle lens, at least without introducing additional higher- and lower-order aberrations as the eye rotates behind the lens.

[Pete Hanlin]

I agree that they are measuring the higher-order aberrations of the eye with their aberrometer, though I would argue that it is mathematically impossible to correct those aberrations fully with a spectacle lens, at least without introducing additional higher- and lower-order aberrations as the eye rotates behind the lens.
In a nutshell, I'm sure that's the question folks from Ophthonix hear most often (I know that's the one I asked them during their SILMO presentation a couple years ago).

Without attempting to speak for another company, the reply I recall was something to the effect that the visual axis usually remains relatively close to the center of the lens.

While I can accept that the eye probably does stay within a few mm of the OC (especially when looking steadily at a distance object- such as a TV or a road at night), the question then becomes one of how the lenses are fit. I would imagine to have any benefit the frames would have to be fit with zero pantoscopic tilt with the OC positioned directly in front of the eye.

I've been measured on the iZon (aberrometer) machine, which indicated I have significant spherical aberration in my cornea (not surprising, since I had LASIK 5+ years ago and have noticed some aberration at night). I'm hoping to try the Ophthonix lenses at some point (unfortunately, they "don't trust" the readings they get at Expo- so I have to make it to an office with the equipment)- just to see if there is any observable improvement in my night vision.

[Darryl Meister]

While I can accept that the eye probably does stay within a few mm of the OC (especially when looking steadily at a distance object- such as a TV or a road at night), the question then becomes one of how the lenses are fit. I would imagine to have any benefit the frames would have to be fit with zero pantoscopic tilt with the OC positioned directly in front of the eye.

I do agree that the line of sight remains within, say, 14 or 15 degrees of the optical axis of the lens under static viewing conditions. Head- and eye-tracking studies have demonstrated that this is a reasonable cut-off before the eye begins to execute a compensatory head movement. (In fact, +/-15 degrees (30 degrees total) is almost exactly the width of a sheet of paper at 40 cm reading distance. However, at the spectacle plane, this represents a total range of over 13 mm, which is easily up to 3 pupil diameters under typical lighting conditions. And vertical head rotation probably varies depending upon both the person and the viewing task.

Now, if the line of sight moves just one-half of a pupil diameter from an "ideal" correction, the induced aberrations around this "sweet spot" exceed the level of correction provided within the "sweet spot." That is to say, if the eye moves just a few millimeters from the center of a zone that has been perfectly corrected for higher-order aberrations, you can actually introduce higher levels of aberrations than you eliminated within the zone, itself. Of course, this isn't to suggest that Ophthonix is providing an "ideal" correction at any point on the lens; they have been very vague about how their lenses actually work, as far as I can tell.

Also, keep in mind that this all assumes the lens has been exactly centered in the first place. Do they require monocular PD and fitting height measurements for their single vision lenses?

[drk]

Pete, if +0.75 back surface add is good, I'm sure the logic dictates that the full add on the back is very, very good.

I've tried to experiment with a pinhole...field of view with 1 mm pinhole smashed into eye socket (vertex ~ 0) is roughly 15 degrees at 40 cm...

...drops to ~half of that @ ~+5 mm vertex distance...very dramatic...

...certainly this reduction in field of view is linear with vertex distance...

...but certainly aperture size is another variable, and that probably is non-linear...(thinking exponent of 2, since area seems to work that way...)

Who knows how much additional field of view a ~15 mm wide near zone aperture gives with an ~5mm reduction in vertex distance? Can't be more than the order of 10-30%. Not peanuts, though...

Totally unrelated visual science thought: Darryl, I noted that you say studies show that if the peripheral object if regard is within approx. the central 30 degree visual field, no head movement is made to fixate the object, but only an eye movement.

Interestingly, we seem to have arrived at 30 degrees as the "gold standard" for visual field testing in perimetry, as well.

Synthesizing all this, it's almost as though if a peripherally viewed object falls within our favorite 30 degree from fixation field of view, we will acquire it with a simple eye movement, but if the peripheral object is outside the 30 degrees, we will know to move our head, too.

Just fun stuff.

[dbracer]

I'd hate to see wavefront correction referred to as "refractive surgery technology," simply because this technology was around long before refractive surgeons ever started using it.

I'm sure you're right. I just never paid much attention to it until they started doing "laser retinal bounces." I've only worked in medical optics. Have some of you worked in device optics like telescopes, microscopes, binoculars etc? Always thought such things would be interesting.

I like what I do, but I'm in private practice in a rural area. And sometimes...the stress of bleeds, trauma, glaucoma, tumors, corneal melt-downs etc. makes me long for just working with optics.

While wavefront-guided ablation certainly minimizes the wavefront aberrations traditionally produced by the refractive surgery, itself, such as spherical aberration, clinical studies have demonstrated that postoperative results are frequently no better than the patient's best corrected acuity prior to surgery.

Well said, and the good surgeons, at least the ones with whom I work, recognize that fact.

You could also say that the "distortions (or at least complaints) of shape perfection" was why the surgeons started looking at wave front analysis more closely. Such complaints are expensive.

I have a 25-year-old book from Mo Jalie that discusses these optical principles in detail.

I've only recently paid attention to this guy's stuff. Mo Jalie ain't your run-of-the-mill light bender.

Respectfully,
dbracer

[dbracer]

Hey drk,

I think you may have some pretty good questions here. I just don't quite understand them -- not that I have the answers.

Could you expound a little?

Respectfully,
dbracer

drk,

Okay you don't have to address my question. These guys are clearing-up your points quite nicely for this rather dim wit.

Respectfully,
dbracer

[Darryl Meister]

Have some of you worked in device optics like telescopes, microscopes, binoculars etc? Alway thought such things would be interesting.

No. But I did sleep in a Holiday Inn Express last night. ;)

Seriously, though, I am reasonably familiar with telescope optics from a project I did for an astronomy course in college (knowing basic telescope optics was also required for my Master certification). And I've become very familiar with the application of adaptive optics for phenomena such as atmospheric turbulence over the past few years, as well as the application of aberrometry for higher-order ocular aberrations.

Mo Jalie ain't your run-of-the-mill light bender.

He is a very friendly, well-spoken person though -- and probably one of the most knowledgeable folks in the field.

[Andrew Weiss]

I've been measured on the iZon (aberrometer) machine, which indicated I have significant spherical aberration in my cornea (not surprising, since I had LASIK 5+ years ago and have noticed some aberration at night). I'm hoping to try the Ophthonix lenses at some point (unfortunately, they "don't trust" the readings they get at Expo- so I have to make it to an office with the equipment)- just to see if there is any observable improvement in my night vision.

I'll be interested to hear what your experience is of wearing the lens. A little real-world test group of one ;).

[dbracer]

Oh Boy, I gets to find out something completely off the subject but I've always wanted to know.

Is Mo Jalie pronounced -- Moe Jol'ly or Moe zhau li' ??

I've alway said the latter, but just because I like it better.

Respectfull,
dbracer