Flitcroft paper on "stair-case" change in refractive status

Discussion in 'Optometry Archives' started by Otis Brown, Jul 10, 2004.

  1. Otis Brown

    Otis Brown Guest

    To: Friends

    From: Otis Brown

    Subject: Vision paper on myopia "staircase" effect.

    Here is the paper that shows the "stair-case" response
    Of the natural eye to:

    1. A confined visual environment.

    2. The effect of a series of increasingly stronger minus lenses,
    to match the "induced" negative refractive status.

    3. The result is that the "step input" is the minus lens,
    and the response is exponetial (e ^ -t/Tau) "cusps", which is the
    response you would expect from an automatically focused
    camera that gains its "input" from the accommodation SIGNAL.


    Best,

    Otis

    *****

    Pergamon -- Vision Research

    Vision Research 38 (1998) 2869-2879


    Flitcroft Vision

    A model of the contribution of oculomotor and optical factors
    to emmetropization and myopia.

    D. I. Flitcroft

    Institute of Ophthalmology, University College Dublin 60
    Eccles Street, Dublin 7, Ireland

    Received in revised form 15 December 15, 1997

    Abstract:

    The purpose of this work was to investigate quantitatively
    the interactions between accommodation, vengeance and a mechanism
    of emmetropization driven by optical blur within the retinal image
    with a view to developing a model that provides an explanation of
    both normal emmetropization and near-work associated myopia. The
    simulations of the change in the refractive state of the eye over
    time that derive from this model indicate that optical regulation
    of eye-growth can result in emmetropization, i.e., a progressive
    reduction in refractive errors over time leading towards
    emmetropia.

    This occurs when viewing conditions involve a preponderance
    of distance work. With increasing near work, the model predicts
    that the refraction of the eye will converge towards myopia. In
    keeping with the previously reported associations of myopia with
    esophoria, poor accommodation function and high AC/A ratios, these
    conditions increase the amount of myopia produced under intensive
    near viewing conditions but do not lead to myopia during mainly
    distance viewing.

    The model provides quantitative validation of the hypothesis
    that the epidemiological association between myopia and increased
    near-work may be caused by a disturbance of normal emmetropization
    by steady state errors of accommodation.

    The same model can explain normal emmetropization, increasing
    myopia with increasing near-work demands and the currently
    recognized oculomotor associations that have been reported to
    precede the development of myopia.

    Elsevier Science Ltd.


    Keywords Accommodation, Vengeance; Myopia; Emmetropization

    ___________

    The paper is covers 11 pages.

    I received it from Dr. Dave Guyton at JHU.

    _____________

    Figure 9

    Graph showing the change in refractive (vertical axis) over
    repeated interactions (horizontal axis) from a starting refraction
    of +2 D with other parameters as for Fig 4a. The dotted line
    shows the change in refraction without spectacle correction and
    the dashed line shows the effect of progressive correction of the
    induced myopia (spectacle correction shown as solid line).

    Figure 10

    Graph showing the change in refraction (vertical axis) from a
    starting refraction of +2 D with other parameters as for Fig. 4a.
    The dashed line shows the change in refraction with a -0.5 D
    correction from iteration 20. The dotted line shows the effect of
    a -0.5 D distance correction with a +1.5 near addition.
     
    Otis Brown, Jul 10, 2004
    #1
    1. Advertisements

  2. Otis Brown

    Dr. Leukoma Guest

    I'm glad that Otis brings up Flitcroft. You will also notice that he
    selectively quotes from a paper published in 1997.

    I would now like to quote from a paper published in 2004, by RA Stone and
    DI Flitcroft, entitled Ocular Shape and Myopia (Ann. Acad. Med. Singapore,
    vol. 33):

    "The insight that normal refractive development is regulated by visual
    quality has diminished the likelihood that accommodation comprises a
    primary mechanism for the cause of myopia... Bifocal and varifocal lens
    treatments, at least with protocols adapted to date, have either revealed
    NO reduction of myopia progression OR a stasticially significant reduction
    that is too small in magnitude for clinical import."

    You see, friends, even Flitcroft recognizes that new scientific information
    requires a re-adjustment in one's thinking.

    DrG


    (Otis Brown) wrote in
     
    Dr. Leukoma, Jul 10, 2004
    #2
    1. Advertisements

  3. Otis Brown

    LarryDoc Guest

    Excellent! That is one helluva "got you" there!

    You see, folks, the difference between SCIENTIST and ZEALOT is indeed
    clear. Otis, now matter how many times he is shown *science* will retort
    with the typical "zealot response": "stop confusing the issue with the
    facts! I know what it true because I understand the *true* workings of
    the system."

    And then: "There's a conspiracy to support the wrong conclusions."
    And then: selectively chosen, often ancient (but since
    adjusted/corrected) reprints, often out of context, in the continuing
    struggle to support unsupportable claims.

    The definition of a zealot.

    Go, Otis. Go. Show us more BS. Or better still, just go away.

    --LB
     
    LarryDoc, Jul 10, 2004
    #3
  4. Otis Brown

    Cathy Hopson Guest

    Wow! I hadn't realized Otis was advocating bifocal and varifocal lens
    treatments to restore unaided distance acuity. Thanks for the
    clarification!

    I assume by your quoting Flitcroft's 2004 article that you believe "normal
    refractive development is regulated by visual quality". I didn't get
    further than the abstract on PubMed, so I will trust your presentation is
    from the body of the article and is not out of context. So, what is
    providing the visual quality? From further in your quote, it would seem to
    be bifocals. Therefore, the bifocals are regulating normal refractive
    development. The outcome of "NO reduction of myopia progression" should
    have been predicted precisely because of the control taken by the bifocals
    for distance viewing, near work not being the issue in myopia. A second
    point I note is that visual quality is suspected, by insight, to push
    accommodation out of first place as a "mechanism for the cause of myopia".
    Leaving it, potentially, as a secondary mechanism?

    The "new scientific information" described in the abstract was that RA Stone
    and DI Flitcroft are interested in "incorporating the 3-dimensional
    conformation of the eye into future clinical studies". They gave no hint
    that they've changed their minds about their 1997 conclusions. Is the
    abstract off-base as to the thrust of the paper? Your reply will help me
    decide the usefulness of PubMed.

    Thanks,

    Cathy
     
    Cathy Hopson, Jul 10, 2004
    #4
  5. Otis Brown

    Dr. Leukoma Guest

    I quoted from the text of the full article. And, yes, Otis is (in)famous
    for promoting plus lenses for the prevention of myopia, and often quotes
    studies involving progressive lenses, accommodation, minus lens-induced
    myopia in order to promote his theories.

    As to the rest of your questions, I will deflect the intellectual energy
    for answering them back into your court.

    DrG
     
    Dr. Leukoma, Jul 10, 2004
    #5
  6. Otis Brown

    Dr. Leukoma Guest

    Cathy, let me add one more comment.

    I am not saying the Flitcroft changed his position entirely, because his
    earlier assertions were quite specific regarding AC/A ratio and nearpoint
    esophoria, which Otis ignores entirely. IMHO, Flitcroft left lots of
    wiggle room with respect to myopiagenesis, and I think he was trying to
    spread his theories too thinly over too much data. The "bandpass" idea
    does leave room for a "visual quality" etiology, which the latter paper
    advances.

    DrG
     
    Dr. Leukoma, Jul 11, 2004
    #6
  7. Otis Brown

    Cathy Hopson Guest

    Bifocals for myopes are not plus lenses. They are minus for distance and
    less minus for near work. -4.00 +1.75 = -2.25, a net minus. One can't
    credibly say plus lenses don't work when the studies that have been cited
    used less minus.


    and often quotes
    As does Flitcroft.
     
    Cathy Hopson, Jul 11, 2004
    #7
  8. Otis Brown

    Otis Brown Guest

    Dear Cathy,

    Subject: Assumptions you have made about the Flitcroft
    paper and interpertations.


    The ODs on this site asked me to post a paper discussing
    the effect the minus lens has on the refractive status
    of the natural eye.

    That is the reason I posted the paper -- not that I
    agree with the WORDING used in the paper.

    I simply state that a sophisticated auto-focused camera
    that controls its refractive status to the ACCOMMODATION
    SIGNAL, will evince a "stair-case" change if a minus lens
    is placed on this auto-focused camera.

    From a "cybernetic" point of view, this is what you would
    expect from a competent control system. It is a matter
    of "jumping the gun" to call refarctive states you don't
    like "defects" and the like.

    This perspective is called a "paradigm" in fundmental
    science. The two paradigms are a "box camera" model
    developed from "standard practice", and of course
    a cybernetic model -- that respects the design
    of this physiological control system.

    Some additional commentary.



    Cathy -- I do not advocate this approach. I advocate that a
    person be informed of the POSSIBILITY of using the plus
    at the 20/40 level (still passes the Snellen-DMV line) BEFORE
    he (a pilot) begins using a minus lens. This would elliminate
    any "bi-focal" or vari-focal lens -- and place the decision
    and "control" in the person himself.


    Cathy > Thanks for the clarification!
    No I do not. I believe that the natural eye controls its
    refractive status to the accommodation signal -- which
    is a reasonable expectation.


    I didn't get
    Otis> I quoted the part of the paper showing the "step" produced
    by the minus lens and the ( e ^ -t/Tau ) response. I simply do
    not have a scanner, and only posted the part of the paper
    discussing the effect of repeated increases in minus lens
    strength would have on the refractive state of the natural eye.

    So, what is
    Cathy, pleas read my paper on "A cybernetic model of accommodation".

    As long as the lens is within the "stop-to-stop" movement
    of the lens -- the image on the retina is perfectly clear.
    Excellent quality.

    From further in your quote, it would seem to
    Otis> If you read my site, you would undertand NO BI-FOCALS.
    The goal is to have the pilot clear his distant vision
    BEFORE there is a requirement that he wear a minus lens
    AT ALL. He must understand this personable responsibility
    and take it seriously.


    Therefore, the bifocals are regulating normal refractive
    Otis> The natural eye will change it refractive state
    in a negative direction if you place a minus lens
    on it (primate eyes).

    The outcome of "NO reduction of myopia progression" should
    Otis> That is a matter of strong disagreemen. I depends
    on WHO ran the study. I do agree that once you begin
    wearing a minus lens -- you will not be able to
    clear by use of a plus lens.

    A second
    Otis> I never said anything about "defect". In the first stage
    where the refractive status is -1/2 diopter (20/40) I would
    expect that by drastic change of the near enviroment with
    a plus lens (changing the average visual enviroment) will
    result in the pilot verifing that he can personally
    see his distant vision VERY SLOWLY CLEARING back to
    20/20 -- and a positive refractive status of some degree.
    I have posted reports of pilots who have already done
    this on my site. Believe it or not.
    They need to apply for further funding for this work -- and
    the application must "please" the ophthalmology department.
    Yes, I understand this process.


    They gave no hint
    Otis> You can and will arrive at you own conclusions on that question.


    Your reply will help me
    Otis> The most important quality you have is your ability
    to look at conflicting ideas -- review what you believe
    is the "correct" experimental data -- and draw
    you own conclusions.

    Best,

    Otis
    Engineer
     
    Otis Brown, Jul 11, 2004
    #8
  9. Otis Brown

    andrew Judd Guest

    Cathy

    I have sometimes worn plus lenses over the top of my distance minus
    lenses to do prolonged periods of close work. This kind of plus
    lens use was advocated by James Arthur
    http://members.aol.com/myopiaprev/improvin.htm who for years was
    trying to remove his myopia. He finally concluded that beyond a 1.5D
    improvement he was never going to get more improvement. So must of
    us would consider varifocal lenses to be plus lens therapy.

    However this is all a distraction for me, I dont believe that myopia
    has got much at all to do with glasses.

    You began your posts to Dr Leukoma with an apparently triumphant
    celibration that finally you could now understand what Otis was
    talking about.

    As wacky as it might seem, I believe that this kind of indirect
    communication is related to being myopic.

    In myopia there can be a tendency to publicly be a wee bit aggressive
    towards others, while actually privately being rather timid or shy.

    Visually, in myopia, our focus of attention is close to ourselves.

    Myopia seems to arise after stressful experiences in our lives, often
    happening at times in our lives when we are vulnerable and have little
    control or power to change things around us.

    Rather than the environment changing, we changed.

    Unfortunately to improve myopia it is not the visual environment that
    now has to change!

    :-(

    Andrew
     
    andrew Judd, Jul 11, 2004
    #9
  10. Otis Brown

    andrew Judd Guest

    andrew Judd, Jul 11, 2004
    #10
  11. Otis Brown

    Cathy Hopson Guest

    Twice the blur at 20 feet and none at 13 inches.

    But accommodation is associated with myopia. Less minus doesn't break the
    association. Zero or plus does.


    but to apply "plus" equally to people of
     
    Cathy Hopson, Jul 11, 2004
    #11
  12. Otis Brown

    Dr. Leukoma Guest

    Accommodation is associated with close work. The purpose of posting
    references to Flitcroft and others was to show how the association between
    accommodation and myopia may not be as significant as once thought.

    DrG
     
    Dr. Leukoma, Jul 11, 2004
    #12
  13. Otis Brown

    Cathy Hopson Guest

    Not as significant as the "primary mechanism for the cause of myopia"
    because they're thinking image quality regulates eye size and shape which, I
    humbly submit, the lens has to accommodate for at all distances. Does that
    work? Not being the cause doesn't eliminate it as big trouble.

    Don't worry, I'm reading through the magazine. I don't want to miss
    anything.

    Cathy
     
    Cathy Hopson, Jul 11, 2004
    #13
  14. Otis Brown

    Jan Guest

    Otis, may I ask......

    This concerns ONE eye of an adult for simplicity reasons..

    Can we agree such a sophisticated auto-focused camera has a certain focal
    length when the lens is adjusted for infinite?
    Can we agree such a focal length has an according power in diopters?
    Can we agree putting a minus lens in front is causing a change in the total
    refracting power of the unit cameralens + minuslens?
    Can we agree the total power of this system (cameralens+minuslens) is lesser
    plus?
    Can we agree the cameralens has to be moved further from the receiving
    (film) plane in this situation ore has to become more plus when wanting a
    sharp image?
    Can we agree this more pluspower can be controlled by a sophisticated system
    and the addition should stop at the moment the control mechanism says
    "sharp" ?
    Can we agree taking away the minuslens causes the sophisticated control
    mechanism to "look" in which direction the sharp image disappeared, forwards
    or backwards and go back to the correct focal distance?

    Then please recognize a "negative feedback mechanism" in both the eye and
    the camera, NOT the positive one you wanted people here to believe.

    Jan (normally Dutch spoken)
     
    Jan, Jul 11, 2004
    #14
  15. Otis Brown

    Dr. Leukoma Guest

    I suspect you are lost in the maze of imprecise knowledge and imprecise
    definitions. Please keep reading.

    DrG
     
    Dr. Leukoma, Jul 12, 2004
    #15
  16. Otis Brown

    Dr. Leukoma Guest

    Most studies cite greater myopic progression in children with greater lag
    of accommodation, which is associated with higher AC/A ratio, and greater
    convergence - i.e. esophoria. The COMET study reported a small, but
    significant effect of progressive addition lenses in these patients. It is
    as though in order to maintain single binocular vision, the patient has to
    give up accommodation, which leads to increased retinal blur.

    However, as the Stone/Flitcroft paper says, there are other causes of
    retinal blur, such as spherical aberration and coma, which are due to the
    shape factor of the eye. This could be one reason why plus lenses are only
    minimally effective at best.

    DrG
     
    Dr. Leukoma, Jul 12, 2004
    #16
  17. Otis Brown

    Cathy Hopson Guest

    .... where I found you. I'll take this as a cordial "Welcome to my world."
    and politely reply, "Thank you." ;)

    Cathy
     
    Cathy Hopson, Jul 12, 2004
    #17
  18. Otis Brown

    Otis Brown Guest

    Dear Dr L,

    You keep on "putting words in my mouth" that I have
    never said, and ASSUMING many things about me
    that simply are not true.

    I am well aware of the "Accommodation-Convergence/Accommodation
    ratio -- but it is not particularaly relevlant as to
    the focal control actions of the natural eye.

    The design of the AC/A ratio is discussed effectively
    by John Semmlow and Georg Hung in their published
    papers.


    Best,

    Otis
    Engineer


    Otis> Please read the above remarks.

    IMHO, Flitcroft left lots of
     
    Otis Brown, Jul 12, 2004
    #18
  19. Otis Brown

    Cathy Hopson Guest

    Francine,

    In case this post wasn't merely a test of Mike's forthrightness, he gave
    this answer in the lens/distance thread: "One over distance in meters".

    Cathy
     
    Cathy Hopson, Jul 12, 2004
    #19
  20. Otis Brown

    Cathy Hopson Guest

    Sorry, I should have continued ...

    From there it's just math. Without glasses, a -6.00 myope can focus at
    approximately 6.5". 1/(6.5/39.4) = 6.00. At what distance does your myope
    want to focus through the weaker part of his bifocals? Plug in your number
    for the net minus needed required for that distance. If 14.25",
    1/(14.25/39.4) = 2.75. To get from -6.00 to -2.75 you add 3.25. Any weaker
    than a net -2.75, and your -6.00 myope will be able to see farther through
    the weaker part of the bifocals, but will be accommodating more (possibly an
    imprecise term) to focus at 14.25". Of course, when he can't see anything
    farther than 14.25" through the -2.75 part, he'll use the -6.00 part and
    accommodate as necessary at the intermediate distances.

    Cathy
     
    Cathy Hopson, Jul 12, 2004
    #20
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.