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Thread: Article on Wavefront Aberrations and Spectacle Lenses

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    Master OptiBoarder Darryl Meister's Avatar
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    Article on Wavefront Aberrations and Spectacle Lenses

    Two-part article on "Wavefront Aberrations and Spectacle Lenses" published in the UK's Dispensing Optics journal:

    Wavefront Aberrations and Spectacle Lenses
    Darryl J. Meister, ABOM

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    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Outstanding!

    My questions are:

    1.How would optimizing someone's HOA's for their spectacle lenses used for driving at night (larger pupils) compare to rountinely adding or ensuring that their refraction is optimized spherically for full driving focus, i.e., not rountinely allowing between 0.12 and 0.25 undercorrection, which is common with today's refractions?

    2. How stable are someone's HOAs?

    3. How does "neural enhancement" of defocussed retinal images play into this discussion?

    Thanks for your terrific explanations, Darryl!

    Barry

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    Quote Originally Posted by Darryl Meister View Post
    Two-part article on "Wavefront Aberrations and Spectacle Lenses" published in the UK's Dispensing Optics journal:

    Wavefront Aberrations and Spectacle Lenses
    Great article, I love the way you have simplified the subject. I have always had a question about how to differentiate HOA and LOA, wouldn't it be technically possible to determine how much HOA is present in a script by comparing refractions done with various pupil sizes. For instance if a refraction was done with lights in the room fully on and the pupil at 4mm and then the same refraction done with the lights dimmed with the pupil at 6mm the difference in the spherical equivalent could be used with the difference in the pupil size to come up with a value using the equation you laid out in your paper.

    SE = [-4*Sqrt(3)]/p^2 Cmn

    Of course it would be more a sum of all the higher order HOA's, which could also be used to determine the RMS error. I could see a dilated and un-dilated exam for comparison as well.

    My reason for asking is this, if the patient has more HOA's present then wouldn't that mean they would experience less acuity from "best form" than someone with less HOA's and consequently wouldn't there be a separate "best form" that would suit the patients particular situation providing better visual acuity? The company iZon had a aberrometer, I could see the future of refraction separating out the HOA and LOA and using the HOA's to design "Super Best Form" lenses for patients. I would love to hear your thought's or if you think I am crazy here.

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    Master OptiBoarder Darryl Meister's Avatar
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    Thanks for the positive feedback, Guys. I'm glad you found the article informative.

    Quote Originally Posted by Barry
    How would optimizing someone's HOA's for their spectacle lenses used for driving at night (larger pupils) compare to rountinely adding or ensuring that their refraction is optimized spherically for full driving focus, i.e., not rountinely allowing between 0.12 and 0.25 undercorrection, which is common with today's refractions?
    I guess it depends upon the particular rationale behind leaving the eye arbitrarily undercorrected or how you choose to define "full driving focus."

    At night, several factors can influence visual clarity. In particular, the larger pupil size makes the eye more sensitive to high-order aberrations. Dark focus or empty field myopia also becomes a factor, as does the Purkinje shift in wavelength sensitivity due to chromatic aberration.

    Quote Originally Posted by Barry
    How stable are someone's HOAs?
    This varies from individual to individual. Also, the contributions of some components of the total high-order aberrations of the eye may remain more stable than the contributions of other components.

    The contribution of aberrations due to the structure of ocular components, such as the asphericity of the cornea or the decentered optics of the eye, should remain fairly stable. The contribution of aberrations related to physiological mechanisms like accommodation or tear break up may vary in predictable patterns. Small aberrations due to fluxations in blood sugar levels, intraocular pressure, etcetera may also result in small changes to the total high-order aberrations of the eye over time.

    Quote Originally Posted by Barry
    How does "neural enhancement" of defocussed retinal images play into this discussion?
    Certain neurological mechanisms are sometimes assumed when calculating vision quality metrics using wavefront aberrations, such as the directional sensitivity of the retina known as the Stiles-Crawford effect. For Stiles-Crawford, for instance, an "apodizing" filter may be applied.

    I think it would be more difficult to quantify or model mathematically the influence on vision quality metrics of higher level neural processing that occurs at later stages in the visual pathways, although I have no doubt that there are a few vision scientists out there attempting to do so.

    Quote Originally Posted by YrahG
    I have always had a question about how to differentiate HOA and LOA, wouldn't it be technically possible to determine how much HOA is present in a script by comparing refractions done with various pupil sizes.
    I imagine that you could estimate the contribution of the total high-order RMS error by comparing the second-order RMS value at one pupil size to the second-order RMS error at a smaller pupil size. If the eye only possessed second-order (sphere and cylinder) aberrations, the Zernike coefficients would be directly related at different pupil sizes.

    To some extent, simply measuring the differences in sphere and cylinder powers at different pupil sizes would provide some qualitative indication of the presence of high-order aberrations, although the interaction between the low-orer and high-order aberrations can be fairly complex.

    Quote Originally Posted by YrahG
    The company iZon had a aberrometer, I could see the future of refraction separating out the HOA and LOA and using the HOA's to design "Super Best Form" lenses for patients
    I think you are referring to "wavefront-guided" prescriptions, which are a very real possibility. This concept is described in the last section of the second article. You will undoubtedly see more spectacle lenses in the future that rely on this approach to maximize visual performance.
    Darryl J. Meister, ABOM

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    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    I see.

    I think that what we've normally termed "night myopia" is probably primarily the result of dark focus & empty field myopia effects (SA at larger pupils and evolution's resting focus posture). These I would think are somewhat separate from the contribution of HOAs, since age (read: accomodation & pupil size) varies inversely with the amount of "night myopia" encountered (at least, that's my experience in astronomy, where we've done much anecdotal testing with IF binoculars)

    Now, it's clear that these effects plus the contribution of HOAs at the dictated entrance pupil diameter will further complete the picture for calculation & possible correction.

    Thanks again for the time to explain and clarify our questions, Darryl

    Barry

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    Quote Originally Posted by Darryl Meister View Post
    I think you are referring to "wavefront-guided" prescriptions, which are a very real possibility. This concept is described in the last section of the second article. You will undoubtedly see more spectacle lenses in the future that rely on this approach to maximize visual performance.
    In my haste I came to the questions of the first article and made an assumption that the article was over, I missed the second part, I look forward to reading it this afternoon.

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    Darryl,

    You refered to "aberration coupling", which I thought was an interesting term and an idea that was brought to me by one of my reps. My lab rep mentioned that in some cases the eye may have present an equal but negative amount of aberration than the lens, which would cancel each other out, he did mention that this effect would not translate across the entire lens surface. I thought it was interesting when he mentioned it and thought maybe he was just blowing smoke, but your article uses the term "aberration coupling" to define the same principle. I appreciated the view into a future where aberrometers could separate out LOA's and HOA's, but I still have a few questions that remain.

    If an aberrometer were to be used would the LOA's be more stable over a larger range of pupil diameters?

    My guess would be you would still have the shift in light sensitivity during night myopia, to contend with as well as issues with accommodation at night. I could see the lens power being more stable though.

    Great article, I can't remember the last time I had to think about what I was reading it's refreshing to see actual facts used in an article. Please post more articles of yours as they become available, this content is like platinum.

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    Master OptiBoarder Darryl Meister's Avatar
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    If an aberrometer were to be used would the LOA's be more stable over a larger range of pupil diameters?
    Yes, ideally, the low-order aberrations will be more stable, at least in the sense that you might be able to estimate a low-order correction that more closely represents the performance of the eye over a range of pupil sizes.

    My guess would be you would still have the shift in light sensitivity during night myopia, to contend with as well as issues with accommodation at night. I could see the lens power being more stable though
    You will still have to contend with several of these factors, but you can at least better predict the ideal vision correction under scotopic (nighttime) viewing conditions or a correction that provides better vision over a range of viewing conditions.
    Darryl J. Meister, ABOM

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