Several dumb questions

Discussion in 'Optometry Archives' started by Joe Bernstein, Nov 7, 2006.

  1. My questions are "dumb" in the sense that they're obvious, not, I hope,
    in the sense that they're stupid. Here's the deal. I'm trying to find
    out about variations in measurable qualities of the human senses. In
    general, I'm having little luck because neither clinical nor research
    purposes are particularly well served by observation of variations
    that are *better* than normal. (Witness, for example, the persistent
    tendency to treat 20/20 as "normal" acuity even while decrying that
    very tendency; and the fact that tetrachromatic vision has only come
    in for noticeable study in the past decade.)

    Anyway, some specific questions:

    1) Several references I've consulted seem convinced that there's a
    simple mathematical relationship between best corrected visual
    acuity, refraction error (as modified by accommodation where
    relevant), and perhaps things like pupil size, as variables, and
    uncorrected visual acuity, as the output. I've found so far
    two references to actual studies on this matter. One has the
    result that when there is no refraction error, uncorrected visual
    acuity is, surprise surprise, 20/20. (Argh. Smith 1991, IIRC.)
    The other is patented; I haven't looked up the hard copy yet, but
    the patent offers only graphs, not an actual equation. (Lead
    author, something like Holladay or Holliday.) Is the visual acuity
    equation a myth?

    2) What's the deal with myopia, unaccommodated hyperopia, and near
    and distance vision? Naively, I'd always thought that unless myopia
    was insanely bad (as mine is), myopes had better near vision than
    normal; and similarly, that hyperopes had better distance vision
    than normal. I can't find a single hint of this in any reference
    I've consulted. So was I just wrong?
    Fine, wouldn't be the first time. But then why on Earth do
    researchers even bother to *measure* near vision? Supposedly, in
    the absence of a refraction error, it'll be the same as distance
    vision every time, and I've seen multiple studies that confirm this
    for fully corrected acuity. So what's the point with near vision,
    if it isn't improved by myopia and harmed by hyperopia?

    3) Is there such a thing as a better-than-normal extent of the
    visual field? If not, then of the three sources I've now found
    that state the normal extent as 180 degrees, 190 degrees, and 200
    degrees, is any telling anything like the truth? How could anyone
    come up with a 200 degree extent, if there's no such thing as a
    better-than-normal extent and the real normal extent is less? But
    if the real normal extent is 200 degrees, what's with the smaller
    So help me, I've now looked at something like *fifty* books
    and web sites about perimetry without finding *one* reference to
    better-than-normal adult visual field extents. The only thing I've
    found is a claim that an NBA basketball player had a better-than-
    normal visual field extent, in a book I cleverly didn't note and
    can no longer find.
    Is better-than-normal visual field extent tabu, perhaps?
    That Which Must Not Be Named? Is it impossible, as the 180-degree
    guy (online) argues? Or what?

    4) Has anyone done any research at all into variations in human
    night vision since World War II ended? If so, did they come up
    with anything? I see that a library in Tacoma (I'm in Seattle)
    has a thick 1991 book on the subject of night vision, but my budget
    for bus fares is currently zero, so before I go there, I'm hoping
    someone can tell me whether this book is likely to do me any good.

    Thanks. Please feel free to pass this on to other fora if they're
    likelier to produce answers.

    Joe Bernstein
    Joe Bernstein, Nov 7, 2006
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  2. Here's my quick 2 cents worth.

    Yes, this equation is a myth. Refractive error is a very precise
    measurement, that is relatively easy to measure and is easily
    reproducable from trial to trial. Visual acuity is a rough estimate of
    a person's ability to see. Visual acuity is influenced by room
    illumination, distance to the target, skill of the examiner, blur
    interpretation skills of the patient, contrast of the chart, clarity of
    the cornea and human lens, quality of the phoropter or spectacle lens
    being used, etc, etc, etc. Considering variations in power and axis
    of astigmatism, you can have any one of thousands of unique refractive
    errors that yield exactly the same visual acuity.
    Myopes have more magnification at near than an emmetrope does, so he is
    capable of better near acuity than an emmetrope, allowing for variables
    like retinal health and lens clarity, of course.
    See above answer. Myopes have more magnification, but very high myopes
    have stretching of the retina that creates a larger space between cells
    in the macula, which can degrade image quality. So, you are touching
    on one of the true paradoxes of increases image size but
    can degrade the "speed of the film."
    Visual fields have physical boundries like big noses and droopy eyelids
    that account for those variations. In contrast, some retinas are built
    like high speed film with superior peri-macular areas that create a
    very robust visual field.
    Once again, good anatomy and healthy retinas with great vascular health
    can open a field beyond average.
    Human night vision is degraded by a number of factors, including the
    greying of the human lens and a slowing of the retinal electrical
    response during low light conditions.
    Taken in its simplest form, your retinal call responds to a light
    stimulus by "throwing a fisbee" to the other end of the rod or cone to
    stimulate an axxon to send an electrical impulse to the brain, which is
    interpreted by the visual cortex as an image. By age 50 your frisbee
    supply is depleted and your throw is weaker. The resulting image at
    the brain level is therefore reduced.
    doctor_my_eye, Nov 7, 2006
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  3. This is a delayed portmanteau reply. I won't bore you with the sob story
    reasons for the delay, but the portmanteau is because in some cases the
    answers in the three reply posts I've seen differ markedly, and I want
    to address those differences clearly.

    In any event, it seems obvious that I'm not going to get references to
    published material here, yes? OK; I just thought asking here was better
    (at least, more polite) than buttonholing random optometrists or
    ophthalmologists at their offices. What I wanted was not so much
    references as indications of whether it was even still worth *looking*
    for certain categories of information. My thanks for those indications.

    Kept for reference some ways below.

    | Best corrected visual acuity is affected by all the variables you
    | list, but I doub t if there is an accurate mathematical equation.
    | It is a very individual thing influenced by very individual
    | psychological and perceptual factors as well such as propensity to
    | guess.
    | Same comment applies to uncorrected visual acuity.

    "Smith (1991) pointed out that the relationship between spherical
    refractive error and visual acuity becomes highly variable when factors
    such as pupil size, illumination, target type, the threshold acuity,
    instructions to the patient, and the patient's background are not
    controlled. He reviewed a number of earlier studies and concluded
    that a better expression of the relationship was determined by the
    following equation:

    VA = square root of [1 + (K * D * S)squared]

    where VA = visual acuity in minutes of arc, or the minimum angle of
    resolution; K = a constant with mean of 0.83 or 0.85 [?]; D = diameter
    of the entrance pupil in millimeters; S = spherical refractive error
    in diopters.
    "Smith (1991) found a linear relationship between VA and S in
    high errors, for which the equation becomes VA = K * D * S. The
    relationship of visual acuity and refractive error is covered in
    more detail in Chapter 7." (Except that it isn't, actually.)

    This is on p. 637 (bottom of first column and top of second) of
    <Borish's Clinical Refraction>, ed. William J. Benjamin, OD, MS, PhD;
    Philadelphia [et many cetera]: W. B. Saunders Company, c 1998. The
    context is a discussion of fogging, of all things, in the chapter
    "Monocular and Binocular Subjective Refraction" by Irvin M. Borish
    and William J. Benjamin, chapter 19, pages 629-723. Unfortunately,
    and oddly, this chapter's references were not printed in the copy
    accessible to me, though I think I can find Smith's article from
    other references.

    Anyway, my point in all this is that Smith apparently did look at
    the physical variables you two listed, though he then came up with
    a simplistic outcome. I'll clearly have to look at the articles;
    I'd hoped y'all would just say "Oh, don't look at those outdated
    things, it's now well known in the field that Murgatroyd 2004 is
    the Gospel truth." Or, flipside, "Snerf 1999 clearly shows that
    these guys with equations were full of it."

    The psychological variables are obviously trickier. But since the
    equation I'm looking for is one that takes *in* objective refraction
    and best corrected visual acuity, and then spits *out* uncorrected
    visual acuity for the *same* person, I would *hope* that the
    psychological variables would *usually*, more or less, on average,
    cancel out.

    I recognise that "best corrected visual acuity" is, at best, a
    problematic concept with limited relationship to what a person
    can actually see. But on the other hand I also recognise that
    my own life experience is clear evidence that the relationship
    *exists*, no matter how limited. And unlike "good eyesight" or
    "bad eyesight", visual acuity can be quantified, however

    Separately, in article <>,
    Mike Ruskai wrote some correct comments about patents (but I should
    note that I'd seen a legitimate source refer to the article the
    patent was based on, before I saw the patent refer to it, so this
    isn't completely kook material) as well as:

    < Beyond that, you need to remember that 20/20 is *defined* as "normal"
    < vision. There's no coincidence if you end up at that value when you
    < eliminate refraction errors.

    I don't wish to be rude, but this simply isn't true except in an
    unuseful sense. 20/20 is defined as normal in a sense similar to
    the sense in which orange is defined as the colour of an orange; it's
    good enough for lay use, but it's not what the pros mean. See on this
    the discussion of "visual acuity" in pretty much any book that devotes
    a chapter to it, for example the chapter by Ian L. Bailey, chapter 7 and
    pp. 179-202 of the book I already cited. 20/20 means you see at 20 feet
    what you should be able to see at 20 feet, where "should" is defined in
    terms of an angle. This angle is either "minimum angle of resolution",
    in which case it's 1 minute, or "minimum angle of recognition", in which
    case it's 5 minutes, depending who you ask. This is because the letters
    eye charts are built out of are built such that the entire letter
    occupies, at 20 feet, 5' or some multiple or fraction thereof, while
    the individual strokes that make up the letter are 1' wide.

    Pretty much *any* set of statistics on how well people see will
    explicitly note that 20/20 is subnormal for healthy young people.
    The guy Snellen who came up with this system himself acknowledged
    this. In the 1960s, normal American men in their 20s or so could see,
    on average, about 20/15, and a few could see 20/10. See on this
    In contrast, Mike Ruskai answered:

    < I think so, though I've certainly heard that position (and believed it
    < until I grew up and thought better of it).
    < In a normal eye, the focal plane for an object at infinity falls on
    < the retina with relaxed focusing muscles. In myopes, the focal plane
    < with relaxed muscles falls in front of the retina. That means the
    < "infinity" focus is actually set for an object nearer than infinity.
    < The stronger the myopia, the closer the relaxed focus position.
    < That allows an uncorrected myope to see clearly without eye strain at,
    < say, a comfortable reading distance. But there's no more acuity, all
    < else being equal, versus a person who has to accomodate to reach focus
    < at that distance.

    So which of you is right? The one who provides the explanation I already
    know for why my naive view was wrong, or the one who provides an
    explanation I hadn't thought of for why it could be right?

    Fortunately, on this one, elementary optics should help. I didn't like
    optics in high school, and skipped the quarter of college physics that
    covered it. But I can probably relearn enough to pay attention to the
    more challenging parts of Brian Curtin's <The Myopias>. I just didn't
    want to bother if there was no reason to.

    I wasn't able to parse the reply to this by Dr Judy at all. What I'm
    concerned with is "Does myopia improve near vision in any way other
    than bringing the near point closer? Does hyperopia improve distance
    vision in any way at all?" Definining "normal" is part of my inquiry,
    in a sense, but isn't really relevant to this particular question.
    Even if I used the *word* "normal" in stating it.
    OK, all of this makes sense to me... So then the question is whether
    any studies of this variation exist.

    My impression that none do is somewhat strengthened by something I came
    across in a detailed guide to perimetric techniques on the Web.
    Apparently one kind of perimetry - ?Goldmann perimetry - is best suited
    for extent determinations (<>);
    and I can imagine that not everyone has Goldmann perimeters, or some

    But it still mystifies me. Decades, indeed over a century, of studies
    of variation in visual acuity. A single study way back in 1922 of
    variation other than age-related in accommodation. And no studies at
    all of variation in visual field extent, except as caused by disease.

    Unless I'm just not looking in the right place. Volume 5 of <Vision
    and Visual Dysfunction>, general editor Prof. John Cronly-Dillon,
    Boca Raton [et alii]: CRC Press, probably c 1991, has the intriguing
    title <Limits of vision>. For all I know, this contains a detailed
    discussion of the topic; volume 5 is the one volume the library I'm
    now typing from doesn't own.

    Mike Ruskai answered:

    < Were any of those figures justified by testing?

    Of course not. None was even footnoted. Snarl.

    Dr Judy's reply included:

    | See comments above about "normal". In clinical perimetry, a given
    | individual field is compared to a standard collection of fields from
    | similar age subjects with no eye disease and no field defect and
    | statistically compared to see if "normal".
    | So what are you researching? Looking for something like the Guiness
    | Book Record for visual acuity, night vision and field extent?
    | This would be an individual measure not a group finding; try looking at
    | case reports.

    Well, for starters, I'm researching "normal". In this case, is it
    180, 190 or 200 degrees?

    In general, I'm researching the range and curve of variation. I get
    the impression that in things medical, or at least things sensory,
    bell curves are vanishingly rare. The only kind of curve most of the
    books I've consulted seem to acknowledge is one where the maximum and
    the mode are identical, and then there's a tail leading off to the
    minimum: Trichromatism is the norm, dichromatism happens, and
    monochromatism is rare; 20/20 is the norm (or 20/15, or whatever), and
    worse acuity happens; in hearing, back in the 1960s they didn't even
    *test* for hearing significantly better than the standards they went
    in with, even though it turned out that those standards were wrong,
    and they were jettisoned a few years later.

    Repeatedly, I'm finding evidence that this "Normal and bad are the only
    options" thing is *wrong*. Tetrachromats exist. 20/20 is not the norm,
    and anyway you can (perhaps) decompose visual acuity into "best corrected
    visual acuity", which is bell curve-ish, "spherical refraction error",
    which is bell curve-ish, and "cylindrical refraction error", which I
    don't know about. And, well, that standard was jettisoned, but it's
    *still* routine for studies of hearing to begin "My group hears *much*
    better/worse than the [current] standards suggest..."

    I'm aware that there *are* reasons to expect "normal or bad, but not
    good" to happen in human biology. Presumably lots of potential bell
    curves get throttled by evolution or some such. It's just that I'm
    becoming decreasingly convinced that there are as *few* bell curves
    as I'm finding discussed.

    The fact that the only datum I have on super-normal visual field extent
    is an anecdote presumably drawn from some sort of individual case
    report is, from my POV, a *bad* thing.
    Um, I don't understand. You're saying rods and cones slow down as we
    age? Why would this be more of an issue at night? (I'd think anything
    that was more an issue at night than by day would be something that
    differentially affected rods more than cones, no?)

    Anyway, though, I'm interested in variation due to aging, but not only
    in such variation. During WWII, the US Navy and Air Force put a lot
    of effort into finding out stuff about variation in human (healthy
    young male, in fact) night vision, and AIUI what they learned was that
    no two variables correlate: for example, night visual acuity is
    unrelated to all of day visual acuity, dark adaptation time, and, oh,
    night visual field. This is obviously not much of an explanation of
    what variation is found in, well, any of these variables. So what I
    was asking was, do any of y'all know whether any more order has been
    brought into the subject since then?

    If what you're saying is "Yes, and that order is that all the other
    changes depend on slow photoreceptor response times", OK, but I'm
    confused; in that case I'd expect more of them to correlate.

    Anyway, thanks for your replies. Sorry it's taken me so long to say so.

    Joe Bernstein
    Joe Bernstein, Nov 14, 2006
  4. Joe Bernstein

    Liz Day Guest

    Wait a sec. Do humans have tetrachromatic vision? I thought that was
    limited to reptiles, fish, and birds (ie, animals with a 4th cone).
    Help please.

    L D
    Liz Day, Nov 14, 2006
  5. Do a Google search something like...

    tetrachromatism OR tetrachromat OR tetrachromacy OR ...

    well, you get the idea, and, so to speak, you'll find it eye-opening.

    Basically, it appears that I wasn't entirely right about the timing;
    the websites claim that tetrachromatic vision in humans had been
    postulated (but not actually found) as early as 1948. In the early
    1990s, the topic was massively revived by an announcement of an
    Actual Tetrachromat Found in England, and although further real
    reports seem to be less than numerous, the topic remains mildly hot.
    This is probably because it fits in well with that aspect of the
    Zeitgeist that emphasises women's health issues (an aspect that, by
    the way, I approve of). 'Cause, you see, tetrachromatism in men
    would require some rather improbable mutations, but in women it's
    not that big a deal. The only question is how uncommon it actually
    is for a woman to jump through all the relevant hoops.

    In a nutshell, here's the deal. The statistics for men are often
    distorted; it's not unusual to run into offhand claims that 10% of
    men are colourblind, which is bullshit, and relevantly so. About
    2% of European men have either protanopia or deuteranopia, which
    are the two forms of what's known as red-green colour blindness.
    There are various extremely rare phenomena that lead to blue-yellow
    colour blindness or full colour blindness; most of these are equal
    opportunity as to which sex they hit. But most of the BS 10% figure
    comes from two things that aren't colour *blindness* at all, just
    anomalies: protanomaly and deuteranomaly. (The equivalent on the
    blue-yellow spectrum would be tritanomaly if it were demonstrated
    to exist, but it hasn't been; the going theory is that it's a weak
    form of tritanopia, which is the name for full-blown blue-yellow
    colour blindness.)

    Anyway. Protanomaly and deuteranomaly both involve mutations to
    the genes that code for the pigments in cone cells, which in most
    people are the only cells that deal with colour. (A few true
    colour-blind people seem to have made their rods deal with colour
    too, which is evidence of how negotiable our neural wiring is; I'll
    get back to that.) Anyway, the deal is that most mammals have only
    two kinds of cones, one of which lives on a regular chromosome
    (trouble with that causes tritanopia), the other on the X chromosome.
    Twice in the primate order, the X chromosome one has been duplicated
    in mutated form to produce a third kind; hence Old World monkeys and
    apes, including us, have on kind of trichromacy, and howler monkeys
    from South America have a different kind. Well, the part of the
    X chromosome in question seems to be remarkably unstable. For
    starters, the majority of people actually have more than one *copy*
    of the new gene on the X chromosome, though only one per X chromosome
    actually functions. Furthermore, about 4-5% of men (in Europe,
    anyhow) have mutated forms of the new gene (which codes M cones'
    pigments), forms which react more or less differently to colours.
    And another 1% or so have mutated forms of the *old* X chromosome
    gene (coding L cones' pigments), which do the same thing.

    Most of these mutations don't do very much, though. You get people
    with an L cone gene that's like 1% deflected from normal, or an M
    cone gene that basically is 1% different from L cones. The former
    person just sees a few colours slightly differently from the rest
    of us, while the latter is only a smidgen short of being red-green
    colour blind.

    But - hypotheses coming! - *sometimes* the mutated gene lands smack
    in the middle, and can be considered by the eye as a whole different
    colour. In men, this leads to disagreements on complicated colour
    matching tests, but otherwise no big deal: the guy still has three
    colours, they just aren't the same as everyone else's three.

    But... In women, who have *two* X chromosomes, if one and only one
    of those has one of those smack-in-the-middle mutations, then that
    woman suddenly has *four* functioning pigment colours: S cones',
    M cones', L cones', and what's being called H cones'. So! This
    suggests that something like 8% or more of women could conceivably
    be tetrachromats, which makes it astonishing that it took decades
    to find even one, right?

    But the plot thickens. Not only do the odds get greatly reduced
    by the tendency for the mutations to be fairly conservative and
    not do the H thing, but there's also the fact that the woman with
    four functioning *cone* colours doesn't necessarily *see* with them.
    She has to somehow get her neural circuitry wired to expect, instead
    of the three contrasts most of us rely on, four. (I think.) Now, as
    noted way back there, there are people out there whose rods have
    learned to contribute to colour vision, so it's hardly rocket science
    for an H cone to find a way to do so; it's just a question of how often
    it actually happens.

    So there you have it: women with colour vision that puts the rest
    of us to shame. Somewhere between .00001% and 10% of the female
    population. Probably.

    Oh, and it gets even better. A logical implication of all this is
    that *pentachromatic* women are also possible: just find *two*
    pigments that are enough-different from the norm, and give her
    one of each, along with the normal three. This is, however, at
    least an order of magnitude less likely than tetrachromatism, and
    so far, nobody's reported any.

    As I said, there's a lot out there. If you're not interested in
    the Google search, you could also try the Wikipedia article on
    "tetrachromat", which has half a dozen of the most significant
    links listed at the end.

    Hope this helps.

    Joe Bernstein
    Joe Bernstein, Nov 15, 2006
  6. It's a definition thing. The term is semi-accurate. The truely color
    blind you describe would be really blind in daylight, as rods are bleached
    under such conditions.
    Scott Seidman, Nov 15, 2006
  7. Albinos have no cones, are monochromats, and are generally legally
    blind, although they can see in daylight (not completely blind).
    w.stacy, o.d.
    William Stacy, Nov 15, 2006
    Joe Bernstein, Nov 20, 2006
  9. Joe Bernstein

    ruskai Guest

    Hello MIKE.

    Title my grandfather was too MICHAL/MIKE/ RUSKAI

    Milan Ruskai

    Vedúci TPV
    SENZOR, s.r.o.
    Zajacia 30
    04 012, KOŠICE

    Tel.: +421 55 6 747 622
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    Fax.: +421 55 7 291 801
    Mob.: +421 905 404 628
    ruskai, Nov 24, 2006
  10. Joe Bernstein

    ruskai Guest

    Mike Ruskai napísal(a):
    ruskai, Nov 24, 2006
  11. Um, actually, the textbooks that you've criticised me for relying on
    also talk a lot about things like contrast sensitivity and so forth.

    There's a recent study for the Canadian equivalent of the Air Force
    which looked at a whole bunch of possible measures of quality of vision
    in the context of whether these would be useful things to test pilots
    on. Time and again they concluded that the tests weren't ready for
    prime time, so while they *wanted* to be able to evaluate pilots'
    abilities in these areas, they didn't think the existing standards
    were meaningful. See if you wish:
    < CR 2005-142.pdf>
    which is bibliographically speaking <Vision Standards for Aircrews:
    Visual Acuity for Pilots> by Jason K. Kumagai, Sheri Williams and
    Donald Kline ([Toronto]: Defence Research and Development Canada,
    2005). As the title suggests, while their remit was primarily the
    topic of visual acuity, this is also the one area they felt they
    could confidently go forward with, in terms of implementing tests.

    I was particularly unimpressed by contrast sensitivity, which is
    frustrating because it seems perfectly clear that the research showing
    it to be a better measure than visual acuity is on the money. But
    near as I can tell, a measure of contrast sensitivity should be a
    *function* of some sort, not a neat number. The report I just cited
    mentioned a website of a prominent supporter of the CS measure; I
    found that he offered a self-test according to which my right eye is
    crippled (an artifact of my taking some time to grasp how the test
    worked), a variety of articles each of which cited mainly his own
    writings, and various ways for him to make money off interest in the
    concept of contrast sensitivity. Snarl. Reminds me of the personality
    testers, yuck. Anyway, the bogus measures I was offered for my eyes
    amounted to *nine* numbers, based on 27 total questions. I'm tolerably
    confident that this does not lead to a simple measurement.

    So sure, I could read all winter. But in the meantime...
    Sigh. We could keep this up forever, couldn't we? "Does increasing
    myopia correlate with any desirable trait for vision, other than a closer
    near point? Does increasing hyperopia correlate with any desirable
    trait for vision at all?"

    I think your next move is to demand that I define "desirable", right?
    And since your focus is on how I have failed to define "normal",
    presumably you'll find some way to link my non-definition of
    "desirable" with my non-definition of "normal", though I'm too hungry
    right this minute to figure out how.

    So let me just concede the game right there. Already in high school I
    learned that arguments over definitions cannot be won. If you want to
    attack my definitions or lack of them, you're not going to get answers.
    If you have a substantive point here, though, I'm unable to see it,
    and this has consistently applied in the days since you posted, not
    being an artifact of my current hunger. So could you please re-frame

    I'll anticipate in one way though. Please note that *throughout* I've
    been trying, and generally failing, to define "normal" in some partly
    numerical and partly qualitative way. I'm happy to define "normal"
    refraction as emmetropia, because that Makes Sense. I'm not happy to
    define "normal" best corrected acuity as 20/20, because that *doesn't*
    Make Sense; there's no obvious intrinsic reason everyone should hit a
    limit at 1 minarc, and in fact lots of people don't. So I don't claim
    to *have* a definition for "normal" acuity; I need to download some
    statistics and analyse them first, and I haven't gotten to that yet.

    Similarly, since my ongoing efforts to define "normal" extent of visual
    field are continuing to fail (see below), I don't have a definition
    there; but this is not some kind of methodological failure in my
    research, this is simply a failure to find data.

    [Do studies of visual field extent exist?]

    I'm well aware that medical research is driven by Problems. But it
    continually astonishes me that there's so *little* attempt to do what
    you're criticising me for not doing: define "normal". I've now found
    several studies of the development of visual field extent in children,
    that included assessment of adults' visual field extents precisely
    because there are no existing standards. Or at least so I read them.
    See below.

    This, I'm happy to report, is false. Again, see below.

    False to a considerably lesser extent.
    Well, at least the Canadian military doesn't seem to have found it;
    visual field extent is one of the areas they considered and provisionally
    rejected. (The other areas I'm tilting at windmills on are colour
    vision and night vision. For colour vision, I'm done, except for parts
    that involve number-crunching I don't currently have computing capacity
    for, to try to reconstruct gene frequencies from phenotypes. I haven't
    really started night vision yet, and Kumagai + co. actually offered
    useful citations on that topic, as on many others.)
    Too many times.
    Well, so I'd assumed until I started reading about the senses!

    I think what I'm running into, time and again, is the clinical thing:
    "If you're not normal, you're diseased." I've been complaining partly
    because this hides super-normal ability, but also partly because of
    times *normal* ability is poorly defined, as with visual field extent.
    ? I know of the Beaver Dam study. Isn't Framingham the nurses'
    study? You're saying they measure things like visual field extent?
    Thank you. In fact, "population AND variation" was something that
    hadn't occurred to me, though it seems obvious now.

    Doing that with "visual field extent" as the third term got me the chain
    of articles I'm trying to follow now, with steadily decreasing confidence;
    the chain starts with the only relevant PubMed cite, "Normative Values
    for Visual Fields in 4- to 12-Year-Old Children Using Kinetic Perimetry"
    by Martin Wilson, Graham Quinn, Velma Dobson, and Michael Breton (<Journal
    of Pediatric Ophthalmology and Strabismus> 28: 151-153, 1991). That
    paper also included tests of 21 adults. I'd be happier if they had
    tested what I'm actually interested in (extent of binocular field, left
    to right and top to bottom), but if I have to work with what they
    provide instead (extent of monocular fields, upper left to lower right
    and lower left to upper right), I'll settle for that. Anyway, there
    were a bunch of cites in a comment on page 154 that noted radical
    disagreements over when kids reach adult visual field extent basically
    depending on the form of perimetry used; so I went and looked at those.
    So far I've seen two, the later of which pointed me to studies on the
    reproducibility of visual field extent measures in adults; I've now
    looked at two of *those* studies without finding anything resembling
    even *monocular* left to right and up to down, though they do give me
    additional data on the oblique angles the JPOS study offered.

    Meanwhile, it also occurred to me to try the same thing with
    "accommodation" as the third term, and this led me to a couple of
    studies from the <Indian Journal of Ophthalmology>, the earlier
    of which also cites studies from various other parts of the world.
    The later study turned up a statistically significant correlation
    between amplitude of accommodation and refraction error in nascent
    presbyopes, something Kumagai et alii also note, from a different
    source which I haven't consulted directly yet; I did, today, find
    a different study that found that amplitude of accommodation does
    *not* significantly correlate with refraction error in young
    children, but, well, I can't say I'm surprised. Anyway, the
    picture for accommodation is clearly much less bleak than I'd thought.
    Are such journals indexed in PubMed, or do I need to look elsewhere?

    In the interest of full disclosure, I also have found (doing a keyword
    search in the Web of Science, of all things) a study of about a hundred
    people done by a physical anthropologist in Colorado some decades ago.
    Only the abstract is known to the Web of Science, and I can't locate the
    author to find out whether the full paper was published in some obscure
    journal or not; I've written to the physical anthropology association,
    which has just written back saying they can't give me any clues, and to
    the guy's old department, which has not written back. The abstract,
    at least, has never been cited in anything the Web of Science indexes.

    Joe Bernstein
    Joe Bernstein, Dec 3, 2006
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