Dear Charles,

Subject:  Does the eye "change" it refractive state
when you place a minus lens on it.

In primate (scientific) studies, the answer is
a clear "yes".

On sci.med.vision, the majority opinion is no.

You should evaluate the scientific experiments
yourself concerning this issue, because
every time I state simple scientific
proof and truth, one man posts
"wanrings" about basic science.

That speaks of intense scientific bias.

It depends on how you "word" you question.

Enjoy,

Otis

Dear Charles,

Here is Dr. Guyton's statement of
the scientific facts concerning
the effect that a lens has
on the refractive state of
the natural eye -- for
your interest.  I sounds
like your eyes "adapted"
in this manner.

Best,

Otis

________

    We asked Dr.  David Guyton, the Krieger Professor of
Pediatric Ophthalmology at Johns Hopkins' Wilmer Eye Institute, to
discuss how these new findings may change the treatment of myopia
in children and young adults.  -- The Editors

            ***************

      The Physician's Perspective -- David L.  Guyton, MD

    According to old-wives' tales, wearing glasses makes the eyes
worse.    Generations of ophthalmologists and optometrists have told
their patients just the opposite, that the eye's development is
predetermined by genetics and cannot be affected by glasses.  A
growing body of animal and human research, however, suggests that
the old wives were right after all.

    The ability of young rhesus monkeys' eyes to gradually change
shape in response to what they see comes as no surprise to vision
scientists.  Over the past two decades, their studies have
demonstrated that the eyes of young birds, tree shrews, guinea
pigs, and marmosets react to unfocused images by altering their
growth to correct the problem.

    It is highly likely that the eyes of infants and young
children also adapt to what they see.  This adaptation occurs by a
relative change in eye length that works something like this:  As
the front of the eye grows and becomes less curved, images focus
deeper and deeper within the eye.  If the lengthwise growth
perfectly matches the change in the eye's other dimensions, then
images continue to focus on the retina.  If there is a mismatch
and the focus is off by even the thickness of this paper, then
vision will be blurred.  Remarkably, the eye apparently senses
where images focus and compensates when needed.  If light focuses
in front of the retina, the eye will stop lengthening until the
images catch up.  If the focus is behind the retina, the eye grows
in length at an accelerated rate until the retina is "pushed back"
to the correct spot relative to the eye's other dimensions.

    Thanks to this feedback mechanism, the eyes generally
maintain clearly focused images throughout early life despite
dramatic changes in size.

    In addition to eye size and shape, the distance between the
eye and the objects it is viewing also determines where images
focus.    Near objects come to focus behind the retina, but the lens
changes shape and pulls the images forward until they are clear
enough to recognize.  However, they often remain slightly behind
the retina.  This slight mismatch may be the mechanism by which
prolonged close work such as reading can signal the eye to grow
longer.  If such a signal occurs frequently and strongly enough in
early life, the human eye may gradually lengthen and become
permanently focused for near objects.  This produces
nearsightedness.

    Most of the adaptive changes in eye length occur during
infancy and youth, while the eye is still growing in its socket.
When the front of the eye stops growing, around age nine or ten,
any further adaptive change can occur only in the myopic direction
-Ä the eye can grow longer, but not shhorter.  Activities such as
prolonged reading at close distances may cause the eyes to
continue lengthening well into one's 20s.

    If this cycle of incomplete focus and eye lengthening is the
primary cause of myopia, how can we intervene in this process?
Some practitioners believe that limiting the amount of close-up
reading or television watching a child or young adult does each
day may prevent myopia.  These days that is a difficult task.  So
I advise parents to encourage children to hold objects and reading
materials as far away from their faces as comfortable, and to sit
at least three feet away from the television screen.  (Those who
insist on holding books close to their eyes, or sitting a foot
from the television or computer, may already have developed
significant myopia or some other problem that warrants a
professional eye examination.)

    For my young patients with simple myopia, I suggest they
leave their distance glasses off while reading, something I have
always done myself.  A child who cannot see the board at school,
for example, should wear glasses to see the board, but remove them
when reading a book or writing.

<snip>

The folks here, it seems, think that eyeglasses are good for you,
by and large.  Being in the eyeglass business is conducive to that
view.

Well, here is some interesting reading, to help prepare you for
discussions with the O.D.s:

http://www.myopia-manual.de/index.htm

Well, I am just guessing that is the right one.  Maybe there is a
hyperopia manual out there, too.  There is a lot of stuff out there.

--
Dicky

Yes, you have opened an old can of worms here, but I still want to
throw in my 2 cents worth.  It has been established for more than a
century that we all tend to start with juvenile hyperopia, or literally
translated "the farsightedness of childhood."  We grow out of this
natural hyperopia in most cases by about age 6 or 7.  If we are lucky,
we stop right around the proper eye length and we don't need corrective
lenses until we are in our 40s.
Myopes go through their natural hyperopic years much quicker, and then
all bets are off as to when the myopic stretching will stop.  There are
general trends in all studies, such as myopic parents tend to have
myopic kids, and Asians are more myopic than other races.  But, through
all the studies, it seems to come down to the general belief that
myopia is an inevitable byproduct of mandatory public education and the
simple fact that we work at near for thousands of hours more than we
look at distance.  If you recognize that we were "originally built" to
hunt for food on the horizon, kill it and eat it...hyperopia once
ruled.  Then, with indoor plumbing, pennicillan and Playstation
2...myopia has taken over.
So, the belief that we can intervene to stop myopia, I feel, is like
trying to stop the fact that humans have grown progressively taller for
the past 100 years.  Its all about adaptation.  If you give young
myopes plus lenses to cancel their myopia, you might also take them out
of school and send them hunting with a bow and arrow as well.

Yes.  What you are thinking goes against the evidence.  Whether one
accepts the evidence is another matter.  Otis doesn't accept the
evidence, and has constructed a very elaborate illogically- constructed
house of cards to explain it all away.

DrG