Dear Friends,

I personally do not support the use of a "bifocal"
on the THRESHOLD of nearsighdness.  If you are
going to go for true-prevention, then use
a full strength plus -- and avoid the minus.

The bifocal is a poor "compromise".  If you
are going to do someting taking strong resolve -- the
do it "right" or don't do it at all.

If these so-called "bifocal" studies, then
they would "convince" all people.  But this
is not so.  The minus is "priviately" recognized
to be "risky" and the animal studies strongly
indicate this truth -- as stated by
Dr. Dave Guyton.

The second opinion is that you should keep that
minus off your face as much as possible (consistent
with safety).

Further, I am certain that Dr. Guyton would have
no problem with a person wearing a plus for
prevention -- if the person had the motivation
to do it correctly.

Best,

Otis
Engineer

___________________________________

    THE PHYSICIAN'S PERSPECTIVE

       David L. Guyton, MD

   Krieger Professor of Pediatric Ophthalmology
       Johns Hopkins' Wilmer Eye Institute,
        Baltimore, Maryland, USA

Health News


    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 the eye can grow longer,
but not shorter.  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.

    Prolonged reading without glasses shouldn't stimulate the eye to
lengthen any farther than what is needed to comfortably focus the eye
at rest at the customary reading distance.  By comparison, when one
reads through glasses or contact lenses designed to bring the distant
world into sharp focus, the page is focused behind the retina.  This
may prompt another round of eye lengthening with worsening of the
myopia.