In article <1163566175.065334.250770[at]m73g2000cwd.googlegroups.com> ,
Dr Judy <mpace99[at]rogers.com> wrote:

- quote -

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:
<http://pubs.drdc-rddc.gc.ca/inbasket...5-142.pdfwhich 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...

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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
it?

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?]
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Understood.

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.

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

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False to a considerably lesser extent.

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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.)

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Too many times.

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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.

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? I know of the Beaver Dam study. Isn't Framingham the nurses'
study? You're saying they measure things like visual field extent?

- quote -

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.

- quote -

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, writer and clerk joe[at]sfbooks.com
<http://www.panix.com/~josephb/> "She suited my mood, Sarah Mondleigh
did - it was like having a kitten in the room, like a vote for unreason."
<Glass Mountain> , Cynthia Voigt

On or about 24 Nov 2006 00:03:01 -0800 did ruskai[at]senzor.sk dribble
thusly:

- quote -

That makes him the first person I've known about to share my name.

With *my* grandfather, who was born in Hungary, it was spelled
Ruszkai.

Is 'Ruskai' a common last name over there?
--
- Mike

Ignore the Python in me to send e-mail.

Mike Ruskai napísal(a):
- quote -

Hello MIKE.

Title my grandfather was too MICHAL/MIKE/ RUSKAI


----------------------------
Milan Ruskai
ruskai[at]senzor.sk
Vedúci TPV
SENZOR, s.r.o.
Zajacia 30
04 012, KOŠICE
SLOVAKIA


Tel.: +421 55 6 747 622
Tel.: +421 55 6 747 623
Fax.: +421 55 7 291 801
Mob.: +421 905 404 628

Joe Bernstein wrote:
- quote -

Most texts say the prevalance is 8% to 10% of males. Lay people think
lots of wrong things including that wearig glasses makes your eyes get
worse, cataract surgery is done with laser, cataracts are on the
outside of the eye, a stigma is some kind of eye growth and that eye
transplants can be done. Our job is to correct their misunderstanding
not change our definition. I tell people who ask or whose child has
just been discovered to have a colour defect that "the colour defective
see hundreds of different colours, the colour normal see thousands."

- quote -

(major snip of description of various types of colour vision defect)

There are, as you point out, many variations of colour vision defect.
For clinical purposes, the differences are of little value. None has a
treatment. To my mind, the only reason to check colour vision is so
that children know if they will fail a standard screening test as that
has career implications.

For those jobs with a colour vision requirement, some employers will
allow for alternate, task based testing, some only will look at the
plate tests results, some will look at D-15 or similar matching tests.
The bulk of those with anomaly including many anomolous tricromats,
will fail the Ishihara plate test; they need to know that when choosing
a career.

Dr Judy

In article <1163563757.304370.176810[at]h54g2000cwb.googlegroups.com> ,
Dr Judy <mpace99[at]rogers.com> wrote:

- quote -


- quote -

Sure, and I'm not arguing with that, though 10% is still too high for
any population known to me outside of small islands. (A bit more than
8% is the highest I tend to see.) It's just that "10% of men are
color blind" is understood by the same lay people who say it as *meaning*
"One man in ten can't see any colours". Which is Wrong.

- quote -

Depends on the meaning of "fail", and on which anomaly they have.
L4M5 ser180 or M4L5 anomalies ought, by and large, to produce full
trichromatic vision in men. But sure, if the definition of "fail" is
"not the same as everyone else", then they fail. On the other hand,
L2M3 or M2L3 ala180 anomalies, those might as well be red-green colour
blindness, as I said.

In, um, "Genetics of Inherited Colour Vision Deficiencies" by Tom
Piantanida, pp. 88-114, which is chapter 7 of <Inherited and Acquired
Colour Vision Deficiencies: Fundamental Aspects and Clinical Studies> ,
edited by David H. Foster, which in turn is volume 7 of <Vision and
Visual Dysfunction> , general editor John Cronly-Dillon, Boca Raton
[et alii]: CRC Press, c 1991... on p. 93, Piantanida offers the
frequency of "pa" and "pae" alleles, which result in male phenotypes
of protanomaly and "extreme" protanomaly respectively; the extreme
kind is about twice as common as the milder kind, which is also
somewhat rarer than protanopia. Similarly milder deuteranomaly turns
out to be somewhat less common than extreme deuteranomaly, with
deuteranopia *much* less common. (Per him; I know there's less
difference in other studies.)

Seems to me that while the exact assignment of pseudo-alleles such
as M4L5 or such to these categories will vary according to whether
the non-anomalous cone they're being contrasted with is ala180 or
ser180 (6% of M cones and 62% of L cones are ser180, apparently),
*some* protanomalies result in full trichromatism, some in impaired
trichromatism, and some are functionally equivalent to protanopia.
And in fact, what happens when phenotypic protanopes are studied is
that more than half of them turn out to have functioning L cones,
they're just carrying effectively M pigments in them. Anyway, all
of the same goes for deuteranomalies too, except that the milder
deuteranomalies are *much* more contrastive with normal L cones than
the milder protanomalies are, so a woman who's heterozygous
deuteranomalous is, imnsho, much likelier to end up a true tetrachromat
than a woman who's heterozygous protanomalous. (There's only one
protanomaly that I see as likely to produce tetrachromatism, but
something like four or five deuteranomalies. I ignored M cones ser180
in my analysis, but adding them just makes heterozygous protanomalous
tetrachromatism even *less* likely.)

I'm not a geneticist, any more than I am an opt*ist. But my mother
taught me a certain amount of genetics, which she learnt from working
in the labs of, and doing degrees under, a whole passel of Nobel Prize-
winning geneticists; and I did just fine in a genetics course at the
University of Chicago, too. So while my optical assertions above may
be shaky, I'm quite confident in my reading of the genetics involved.

- quote -

Well, that depends on who's doing the defining. Blue cone monochromats,
and for that matter red and green cone monochromats if you believe in
their existence, do have minimal colour vision thanks to rod-cone
contrasts, as I mentioned in my previous post. But the Achromatopsia
Network still explicitly opens its doors to blue cone monochromats at
its home page (<http://www.achromat.org/> ); I don't know if it leaves
out red and green cone monochromats because their putative symptoms
are so much less severe (little visual acuity loss, no nystagmus or
photophobia ...) or because it, like others, considers red and green
cone monochromatism mythical. Anyway, I figure the actual achromats
at the Achromatopsia Network have more right to define "achromatism"
than I do, since I'm just a layman myself, after all. Note that rod
monochromats easily outnumber blue cone monochromats, so this isn't
a simple case of the larger swallowing the smaller.

Several sites devoted to achromatopsia link to, or cite, or etc. one
Sebastian Bonhag of Germany, who's a blue cone monochromat, and who is
inter alia credited with having done the (moderately bad) scan of Knut
Nordby's account of his rod monochromatism which can still be found at
<http://bpeyes.com/achromat.htm> while Bonhag's own site (at
<http://www.bonhag.de/> ) appears to be down temporarily or otherwise.
So the regard rod monochromats apparently have for blue cone monochromats
also appears to be mutual.

Joe Bernstein

--
Joe Bernstein, writer joe[at]sfbooks.com
<http://www.panix.com/~josephb/> "She suited my mood, Sarah Mondleigh
did - it was like having a kitten in the room, like a vote for unreason."
<Glass Mountain> , Cynthia Voigt

On or about 14 Nov 2006 12:11:33 -0800 did "Liz Day"
<beebuzz[at]kiva.net> dribble thusly:

- quote -

Only some women, and only maybe.

The genes that encode for red and green pigments are both on the X
chromosome. Females, of course, get two copies of this chromosome,
and through a strange bunch of hoops may end up with some cells
expressing one copy, while others express the remaining copy.

The upshot is that these women have four different photoreceptors in
their eyes, with the spare being a slight variation of red or green.
They are also more likely to give birth to colorblind sons (because
the chromosome that provides the extra receptor is defective, in that
only one gene - red or green - actually works, and the son has a 50%
chance of getting that defective copy).

I don't believe it has been definitively demonstrated yet whether or
not this actually results in tetrachromatism. It's not enough to have
receptors sensitive to slightly different wavelengths of light. The
brain has to be wired up to make use of that information. So the
green and greenish (or red and reddish) receptors could trigger the
same response in the brain.

By comparison, we have on the one hand some South American primates,
where all males are dichromatic (i.e. what we would call color blind),
and females trichromatic. The females can definitely see in
trichromatic color, so having only one sex to work with is clearly not
an impediment to natural selection wiring up the brain appropriately.

In humans, however, it's only a small percentage of the one sex.

Naturally, it's not an easy thing to determine experimentally, though
there are probably some that try to answer the question that I haven't
read about.
--
- Mike

Ignore the Python in me to send e-mail.

Scott Seidman wrote:
- quote -

And they are. Best corrected acuity in a rod monocromat will be in the
20/100 to 20/200 range with light sensitivity meaning they need
sunglasses.

For detail about colour vision see:
http://en.wikipedia.org/wiki/Color_blindness

Dr Judy

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Albinos have no cones, are monochromats, and are generally legally
blind, although they can see in daylight (not completely blind).
w.stacy, o.d.

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"Dr Judy" <mpace99[at]rogers.com> wrote in news:1163563757.304370.176810
[at]h54g2000cwb.googlegroups.com:

- quote -

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
Reverse name to reply