The results you get with any aberrometer

[Barry Santini]

Clearly depend on:
Pupil size sampled
Homogeneity of the tear film

Discussion please

This is after taking the izon and iscriptor demos

B

[rinselberg]

Not sure where you are going with this.

Doesn't all that (variability due to pupil size and/or tear film) apply equally to traditional or subjective refraction methods?

[Darryl Meister]

Just remember that the results vary with pupil size and the tear layer because the optics of the eye vary with pupil size and tear layer, as rinselberg pointed out. So these effects will also influence other objective measurements of the refractive status of the eye as well as subjective refraction.

The precorneal tear film is responsible for up to 4.00 diopters or more of refractive power. So significant differences in the tear film can affect measurements of the refractive status of the eye. Studies have also shown that the high-order aberrations of the eye can also increase significantly due to the quality of the tear film.

Additionally, the low-order refractive errors and high-order aberrations of the eye depend upon pupil size. When the pupil is small, the optics of the eye are restricted to a relatively narrow region of cornea and lens. When the pupil is large, the focus is the result of a much larger area of the cornea and lens. This effect commonly contributes, for instance, to "night myopia."

Compared to conventional autorefractors, these effects are more obvious with aberrometers, because these instruments are often more sensitive, sample a larger area of the optical system of the eye, and measure the more subtle optical effects of the optics of the eye. In particular, the high-order aberrations that also influence vision quality are measured. Aberrometers often capture these measurements at a higher resolution as well.

Best regards,
Darryl

[rinselberg]

OK, I was thinking "auto-refractor", when what Barry actually said was "aberrometer".

I think that Barry is saying that the higher order or "wavefront" distortions in a patient's vision that an aberrometer measures (including coma, trefoil and spherical aberrations) are so variable--changing as the patient's pupil size and tear film vary from minute to minute throughout the day--that it doesn't make any sense to incorporate these higher order visual corrections into the manufacture of a patient's Rx spectacle lenses.

This calls into question the effectiveness of using "wavefront corrected" spectacle lenses like iZon (from Ophthonix) and the Zeiss i.Scription lenses.

It seems to me that only sound clinical trials with good statistical analysis can provide the answer as to whether using higher order corrections from aberrometer measurements makes any real world difference, as to how the patient actually sees.

We've been over some of this ground before with the many discussions of the iZon "wavefront corrected" spectacle lenses.

I think you have to look very carefully at the clinical trials and see (pun intended) what you make of them.

[rinselberg]

I think it would be worthwhile to review (or even renew) this brief OptiBoard discussion from 2009:

"Like clinical studies? A new one about iZon lenses.."
http://www.optiboard.com/forums/show...ut-iZon-lenses..

[rinselberg]

If you want to read more on line about "wavefront corrected" Rx spectacle lenses:

"i.Scription by Zeiss: Setting the New Standard of Vision Correction"
--Darryl Meister, ABOM (Carl Zeiss Vision) and Larry Thibos, PhD (Indiana University)
http://www.zeiss.de/4125682000258738/EmbedTitelIntern/iScription_White_Paper/$File/iScription_White_Paper.pdf

"The Wavefront Technology Revolution Continues with the iZon™ High Resolution Progressive Addition Lens"
--John Seegers, LDO
http://www.totallyoptical.com/Media/...ger/WaveCE.pdf

[rinselberg]

What is i.Scription® by ZEISS?
i.Scription is a revolutionary method of optical calculation that optimizes a patient’s prescription based upon the total wavefront aberrations of each eye as measured by the i.Profilerplus®.

What is the benefit of i.Scription?
By optimizing the lens for the eye’s total wavefront aberrations, including both the “low-order” and “high-order” aberrations, i.Scription can significantly enhance overall visual performance including visual acuity, contrast sensitivity, and depth perception, particularly at night and in low-light viewing conditions.

Do i.Scription wearers really notice improved vision?
Early clinical results from European field trials indicate three areas of enhanced visual performance with i.Scription lenses including:

74% of i.Scription® wearers confirmed better vision at night and in low contrast situations.

4 out of 5 of i.Scription® wearers surveyed stated that they enjoyed greater visual comfort.

More than 3 out of 5 of i.Scription wearers surveyed saw colors more intensively.

Additional results from a field trial conducted with 416 customers in Belgium/Netherlands showed:

70% of the surveyed wearers experienced crisper, sharper vision with i.Scription®.


What about the details of that field trial..? I don't think that it is available on line. Perhaps it is available by requesting it from Zeiss(?) I think that we would have to scrutinize the details of that field trial before coming to a more informed opinion about i.Scription ...


For more about Zeiss i.Scription lenses:
http://www.vision.zeiss.com/us/iscription

[fjpod]

The problem I have with aberrometry is how does it change the "outcome". Anyone can tell you that a larger pupil at night requires a bit more minus, and you can determine this by darkening the refraction room and doing a duochrome test.

Is it that we just want a technician to be able to do it on an autorefractor like instrument? Is it so we can justify recommending another pair of glasses to the patient for night driving (which we sometimes do already)...and hence, how does it change the outcome? I still don't understand how claims that digital or free-form lenses work better in these situations. Can someone explain it to me?

[Barry Santini]

At VEE, the Iscription demo required:

1. Me to blink regularly before the reading to assure a stable tear film (see above)
2. Inputing of present RX
3. Inputing of subjective Rx

Push calculate button: Voila! The I scriptor uses a proprietary algorthym to deliver the new calculated Rx to a 0.01D precision, and then this is outputted to Zeiss lenses entry, along with POW values if required.

Looks impressive. I'll need more experience before I conclude anything here.

FWIW

B

[rbaker]

How can you derive a definitive "refraction" of the eye when the eye is a dynamic, ever-changing optical system with the refractive state of the crystalline lens and the aperture, among other parameters, constantly in flux. Its sort of like the Heisenberg uncertainty principal. It's interesting from an academic point of view but has little clinical value unless it is used as a replacement for an autorefractor or as a marketing tool.

[Darryl Meister]

At VEE, the Iscription demo required: 1. Me to blink regularly before the reading to assure a stable tear film (see above) 2. Inputing of present RX 3. Inputing of subjective Rx

The present Rx should be transmitted automatically from the i.Profiler to the i.Scription software. The subjective refraction is incorporated into the i.Scription to factor in any sort of binocular balancing or other modifications that the refractionist may have arrived at through his or her clinical expertise. Blinking regularly isn't really a requirement, per se, but we do not recommend it to ensure the most accurate refraction.

The problem I have with aberrometry is how does it change the "outcome". Anyone can tell you that a larger pupil at night requires a bit more minus, and you can determine this by darkening the refraction room and doing a duochrome test.

Because aberrometers precisely assess the complete refractive status of the eye, including the more subtle ocular aberrations, aberrometry has clinical applications beyond simply refracting the eye for a spectacle prescription. Nevertheless, wavefront-guided vision corrections, such as i.Scription, rely on the aberration data captured by an aberrometer to optimize a vision correction that delivers the best vision quality possible for a given viewing condition or over a range of viewing conditions.

Yes, you can attempt to simulate this effect to some extent by refracting the patient in mesopic, low-light level viewing conditions with reduced room illumination and lowered chart luminance. Although the refraction will still be limited by several factors, such as the depth of focus of the eye, failure of the cross-cylinder technique to converge to the best cylinder power, use of loose trial lenses in 0.25-diopter increments, variations in the subjective response, etcetera.

I still don't understand how claims that digital or free-form lenses work better in these situations. Can someone explain it to me?

The i.Scription vision correction is only applied on customized lenses for several reasons:

1) Free-form surfacing is required in order to produce the wavefront-guided prescription powers to the desired level of precision of +/-0.01 D.

2) ZEISS free-form lenses are optically customized to minimize the low-order aberrations produced by the prescription and position of wear, which is important when attempting to improve vision quality further using a wavefront-guided vision correction.

3) Given the emphasis on enhanced visual performance, the marriage of these two optical technologies is logical, and will ensure the highest quality visual experience for the wearer.

How can you derive a definitive "refraction" of the eye when the eye is a dynamic, ever-changing optical system with the refractive state of the crystalline lens and the aperture, among other parameters, constantly in flux.

I don't know that there is such a thing as a definitive refraction, and studies continue to show a significant variance in the refractions performed by different clinicians on the same subject and in the repeated refractions performed on the same subject by the same clinician. But, because of these variations, this is all the more reason to capture the most accurate and precise refraction possible.

Best regards,
Darryl

[Uncle Fester]

Am I the only one who finds this comes to mind?

http://www.youtube.com/watch?v=uXQeWW-Nizs

[Darryl Meister]

I'm certainly no Gregory Hines.

[fjpod]

So, Daryl, if I might take my question one step further...If we use the aberrometer to refract down to the last .01D, and consider the specific task and light levels the patient will use the Rx in, and ANSI standards being what they are,...suppose the patient now uses the Rx for a different purpose, or decides they want to wear it down more on their nose, or they have very high cheekbones and we have to reduce patnto?? What was the sense of getting it down to the last .01? A very expensive free-form lens is now just as inaccurate as any other lens.

[Darryl Meister]

So, Daryl, if I might take my question one step further...If we use the aberrometer to refract down to the last .01D, and consider the specific task and light levels the patient will use the Rx in, and ANSI standards being what they are,...suppose the patient now uses the Rx for a different purpose, or decides they want to wear it down more on their nose, or they have very high cheekbones and we have to reduce patnto?? What was the sense of getting it down to the last .01? A very expensive free-form lens is now just as inaccurate as any other lens.

I cannot speak for the prescription optimization algorithm used by other companies, such as Ophthonix or Marco, but the i.Scription algorithm calculates the sharpest prescription that actually maximizes the depth of focus of the eye. The three-dimensional "blur volume" is minimized in the vicinity of the focus for a medium pupil size. Consequently, rather than optimizing the refraction for a single set of viewing conditions or parameters, i.Scription seeks to maximize visual performance over a range of viewing conditions, light levels, and working distances. You can find details regarding this algorithm in the i.Scription white paper referenced above.

they want to wear it down more on their nose, or they have very high cheekbones and we have to reduce patnto?? What was the sense of getting it down to the last .01? A very expensive free-form lens is now just as inaccurate as any other lens.

If the patient is likely to experience a change in optical performance due to a variety of variables, this is actually justification for achieving the most accurate prescription possible, initially. After all, any unwanted changes to the desired prescription caused by factors such as the position of wear or manufacturing variations will simply compound any errors in the original manifest refraction, resulting in a propagation of error that is even more likely to exceed the depth of focus of the wearer.

Secondly, while the increased precision of the refraction, in 0.01-diopter steps, is certainly an advantage, don't forget about the increased accuracy that may be possible by calculating the wavefront-guided prescription using an exact and sensitive assessment of the entire refractive status of the eye. It is the combination of increased precision and accuracy that tightens the difference between the final wavefront-guided prescription and the most ideal ocular refraction possible for a given patient.

Best regards,
Darryl

[Darryl Meister]

By the way, I feel like I've been monopolizing this conversation on aberrometry and wavefront-guided prescriptions. And I can only speak to the benefits of Carl Zeiss Vision's particular solution. I do hope that someone from Ophthonix, Marco, WaveSource, etcetera, can add his or her own feedback regarding their particular solution to this discussion.

Best regards,
Darryl

[fjpod]

I guess I can go on doubting forever...

Another problem I have with the concept is the fact that after refracting a patient by whatever means, I always alter the final Rx given based on their habitual Rx, level of complaints with it, acuity difference before and after, previous difficulties accepting a cylinder, and a few other things. So again, what's the point of being accurate to the last .01D?

In my mind....the final Rx has more to do with my years of experience and gut feelings than it does with any single piece of data.

[Barry Santini]

I also agree with your sentiments, fjpod. Experience and instinct are important as well. Either way, though, when the person is unhappy, there's a job to be done.

B

[Craig]

If you want to read more on line about "wavefront corrected" Rx spectacle lenses:


"The Wavefront Technology Revolution Continues with the iZon™ High Resolution Progressive Addition Lens"
--John Seegers, LDO
http://www.totallyoptical.com/Media/...ger/WaveCE.pdf

Below is cut from the above presentation; I wonder if John Seegers knows he told a fib?

Just like its single vision companion, iZon Progressive
Addition Lenses consist of a sophisticated wafer system
composed of three portions (Figure 8): a front wafer
constructed of 1.6 high index plastic; a center layer
made of a liquid polymer, called the “iZonik™” layer by
Ophthonix; and a back wafer also constructed of 1.6
high index plastic. The 1.6 high index lens material has
an Abbe value of 42 and a specific gravity of 1.34
grams/cm

3, so it is thin, light weight, and optically clear.
The front wafer contains no power while the back
wafer contains the patient’s sphere, cylinder, axis, and
the progressive lens optics. The central liquid polymer
iZonik layer is is cured and hardened. The patient’s
iPrint data from the Z-View Aberrometer is transferred
to manufacturing equipment at Ophthonix and incorporated

into the iZonik material.

[Craig]

I am interested in the new Zeiss product and am sure it does what it claims. I just need Zeiss to give me a call and I need them to offer trivex.
Craig

[Darryl Meister]

In my mind....the final Rx has more to do with my years of experience and gut feelings than it does with any single piece of data

We agree completely, which is why your subjective refraction is a critical component in the i.Scription calculation.

Best regards,
Darryl