For "Frosty Paw" =-- the -1/3 diopter / year at a military college

Dear FrostyPaw --


Subject: Clarification of the -1/3 diopter per year statement
about the behavior of the natural eye.


You asked for background information on the behavior of the
normal eye at our military colleges.

I stated specifically, that the "downward" rate for all these
eyes was approximately -1/3 diopters per year. This is the average
value for ALL eyes.

Some eyes went "down" at a faster rate, and some showed a
rate of zero diopters. But the AVERAGE of all NORMAL EYES was
-1/3 diopter per year, and obviously -1.333 for four years.

Since FrostyPaw doubted these statistics, I am posting
statements by Dr. R. Hayden about various issues concerning this
basic statistics.

In general, I simply report objective facts. Others can put
their own "spin" on them if the like.

It is often claimed that no one knows how or why the eye
develops nearsightedness -- and no one can "predict" the
development of a negative focal status for the eye for a person
entering college.

If a pilot enters a four year college with 20/20, but a focal
status of zero (sometimes called "emmetropia"), it is virtually
certain that he will not be 20/20 at graduation. The statistics
show that his vision will be -1.0 to -1.3 diopters with a visual
acuity of 20/70 to 20/100. No one ever bothers to tell any pilot
about these statistics. If they only knew they MIGHT be able to
take effective action for prevention.

Here are the records and statement about the eyes movement
from a positive value to a negative value at the Naval Academy.

When we attempted to institute a "preventive" method at the
Naval Academy we go nothing but "stone-walling" of the type you
have seen from sci.med.vision.

When I asked you to use the plus for prevention at college, I
was well-aware of these statistics. It is very hard to miss the
point -- but it seems everyone manages to do so.


Best,


Otis

cc:
Dr. Steve Leung
Dr. Stirling Colgate
Dr. Dave Guyton
Dr. Francis Young



****************


For: Sci.med.vision discussion

Dear Bill,


Re: Dear Otis -- If a person is not myopic by the time they reach
college (USAF Academy) what are the chances of becoming
myopic from the required reading load? Has the USAF run any
experiments to find out what causes myopia in their
personnel? -- Bill

________________________________________


If you know the refractive state of an "entering" student can
you predict the resultant refractive state after four years?

If you check the person's focal status, and find it to be
"zero" or "plano", then the probability the person will retain his
20/20 is about one percent -- as stated by Dr. Hayden.


Note: Refractive state is determined by using a trial-lens kit.
It is first established that the pilot (or entering
student) has 20/20. The next step it to use a sequence of
stronger plus lenses to establish the student's
refractive state as having some positive status.


REFERENCES

1. Reynolds Hayden, M.D., "Development and Prevention of Myopia at
the United States Naval Academy", Volume 25, (old series
Volume 82), Number 4., Copyright, 1941, The American
Medical Association.

2. Gmelin, Maj. Robert T., MSC, USA, "Myopia at West Point: Past
and Present." Military Medicine, 141 (8) 542-3, August
1976.


Here is the information I have on your question concerning
"base-line data" concerning the behavior of the natural and
healthy eye at the Naval Academy.



SYNOPSIS

For years, since 1879 in fact, studies of military cadets in
the United States have shown that their vision changes over the
years of their academic work. Records reveal that a large
percentage of the cadets (39% of those at the U.S. Military
Academy in 1956) [2] became nearsighted and needed negative lenses
by graduation.

Further, of those who developed 20/25 vision, only one
percent recovered to 20/20 over the four years, [1]. (They were
not provided with plus-lenses, and for this reason had no chance
to recover.)

In early years their degraded vision was blamed on the fumes
of gas lighting, and later, on any number of factors, but the
upshot of the studies was that none of these circumstance were
really behind the cadet's loss of visual acuity. The myopia
(change of focal state) was a result of the fact that the natural
eye controls its focal state to its average visual environment.
Roughly, that is looking close, studying, reading, looking at
books, for long periods of time -- rather than at distant objects.


SELECTED STATEMENTS FROM DR. HAYDEN

"...For many years the high incidence of myopia which
apparently developed among midshipmen after admission to the
United States Naval Academy with supposedly normal vision was a
cause of serious concern to all those interested."

(Extended "rest" was offered, as stated by Dr. Hayden)

"...and by retaining may of them (who became nearsighted) in
the Naval Academy for one to three years in the hope that their
vision would improve."

"...In the vast majority of cases their vision did not
improve, and the midshipmen was forced to leave the naval service
after two to four years in the Naval Academy. Experience showed
that only about one percent of such men had 20/20 on their final
physical examination."

[Summary -- if their focal status became even SLIGHTLY
negative (20/25) they had virtually no chance of clearing their
distant vision to 20/20. OSB]

"...Furthermore, an excessive number of junior line officers
were being retired because of defective vision, and the records
showed that the vision of 3/4 of these had become defection
defective (vision less than 20/20 for each eye) at the Naval
Academy."

[Dr. Hayden then reviews the statistics on a class by class
basis -- to long to type up.]

"...Any candidate, however, who if found to have any degree
of myopia following the use of a cycloplegic, even -0.12 or -0.25
diopters is rejected."


NECESSITY OF HYPEROPIC RESERVE

(For young health men with 20/20 -- A
Positive focal state of the eye. OSB)


PARAPHRASE

Review of the refraction of the eye of candidates at the time
of preliminary physical examination showed that the great majority
of candidates whose refraction was of the plano-type, including
+0.25 diopters. At the first year their examination would show
that they had myopia.

Occasionally a candidate who showed as much as +0.5 diopters
"hypermetropia" on preliminary physical examination was found to
have -0.25 diopters of myopia in the first year.


[EMMETROPIA IS DEFINED AS NORMAL OR PERFECT BASED
ON THE DONDERS-HELMHOLTZ CONCEPTUALIZATION -- OSB]

DR. HAYDEN STATES THAT EMMETROPIA IS NOT NORMAL FOR
THE FOLLOWING REASONS

"...As is well known, the emmetropic eye is for practical
purpose an abnormal eye -- the great majority of persons with
so-called normal vision being actually hypermetropic. Those
candidates, then, whose refraction was of the plano (emmetropic --
focal status exactly zero) had borderline conditions definitely on
the way to myopia. For all practical purposes, experience here
has shown that patients with +0.25 diopters of hypermetropia are
in the same class."

[This is why I use the word "focal state" to define what we
measure, rather than implying "defect" for what is in fact natural
an normal. OSB]

"In view of the experience at the Naval Academy during the
past three years as described, it is evident that a reserve of
preferably 1 diopter and at least 1/2 diopter is necessary at the
time of preliminary refraction to be reasonably sure that the
candidate will pass his physical examination for admission."

"Furthermore, in order to be reasonably sure of being
visually qualified for a commission in the line of the Navy after
four years at the Naval Academy -- it is necessary that the
student have a hyperopic reserve of at least one diopter of
hypermetropia at the time of admission."

"Of course, an occasional candidate will +0.25 to +0.5
diopter of hypermetropia at the time of admission will
survive visually and receive a commission, but this is
exceptional."


DR. HAYDEN THEN DISCUSSES ATROPINE A CYCLOPLEGIC

He details the loss of people in various classes who were
"emmetropic" (focal state zero) on entry, using various drugs and
percentage mixtures. It was hoped that using different drugs
would produce better results and these emmetropic eyes could be
"saved". However:

In one case (c, d) the loss was 70 percent after three years,

In another case (c, d) the loss was 85 percent at 2 years.


THERE IS SOME ADDITIONAL DISCUSSION OF ILLUMINATION
LEVELS AND EFFORTS TO IMPROVE THESE LEVELS


CONCLUSIONS

"It is considered that during the past three years the Naval
Academy has definitely proved the necessity of midshipmen having a
"hyperopic reserve" of at least 1 diopter at the time of admission
to the Naval Academy, and of their meeting the present visual
requirements if the visual standards of the Naval are to be
maintained."

"...Any candidate having less than 1/2 diopter of
hypermetropia at the time of a preliminary ocular refraction
should be informed that, while visually qualified at the time, he
has a borderline condition which may progress to a low degree of
myopia by the time he takes his physical examination for admission
to the Naval Academy, and may therefore be rejected."

"Any candidate having from 0.5 to 1.0 diopters of
hypermetropia at the time of a preliminary ocular refraction
should be informed that, while he should pass the physical
examination for entrance to the Naval Academy, he stands no better
than an even chance of visually obtaining a commission in the line
of the Navy on graduation."

____________________________________


Note 1: All these men had healthy retinas. All retinas had the
capability of resolving 5 minute-of-angle targets at 20
feet. Their natural eye's behaved as expected. The
controlled their focal state to the visual environment.
For this reason an "undesired" focal state does no
indicate an "organic defect" or words to that effect.
For that reason I use the term focal state so their is no
confusion in your mind about that point.


Note 2: The words emmetropia and ametropia were introduced by
Donders. Donders took the focal states of the normal eye
to be DEFECTS of the eye. Any non-zero focal state of
the eye was, by definition, a defect (ametropia). A
focal state of EXACTLY zero was defined as "normal".
Under this definition, very few, if any, animals or
humans have eyes that are normal!

 

That's one doctor from a LONG time before I was born - where's a
recent study showing this 1/3diopter shift?

ps. i must clarify that my views are in no way associated with
teletext, i was simply posting from that address and will shortly
change to something more suitable.

 

Dear Mike,

The point you are missing, Mike, is that this is not your
decision.

Your understanding of statistics is poor since you do
not seem to understand the concept of STATISTICAL
AVERAGE for an entire population of NATURAL EYES>

I have greater confidence in engineering students
(who will review this data) than I do in you.

Since prevention is indeed hard work, and
requires a great motivation and insight,
I doubt that your involvement would
serve any purpose in this type of work.

Best,

Otis
Engineer

 

Hayden's 1941 study found about just under 40% of cadets became nearsighted
by graduation, so 60% did not. Since the average myopia of all students is
1.33 and 60% are not myopic, the average myopia must be considerably more,
ie about 3.00D to 3.50D. If, as you propose, the use lof lenses changes
refractive error, then those who use plus lenses and were destined to be
myopes will not be myopic, but those who use lenses and were not destined to
be myopic will then be more hyperopic than they started, presumably by at
least 3.00D. Should you not be warning those students that they may face
much earlier than normal need for reading glasses, likely in their late
twenties to early thirties?

snip

If the method you proposed looked anything like the proposed "study" you
have posted here, with its scientific errors and lack of credible
references, I can imagine that Naval Academy would have politely shown you
the door and thought you to be a kook. Look up the suggestions that various
people here made to you about improving the proposal, make the changes and
try again.

Dr Judy

snip balance.

 

Dear Judy,

Again you miss the point -- as a matter of statistics.

The AVERAGE movement for the entire population of
natural eyes was -1/4 diopter as reported by
Dr. Hayder.

But he was very explicit about the entering midshipman
who had a refractive status of 0.0, i.e., "squinting 20/20".

He said that that person has less than a one-percent
probability of graduating from the Naval Academy
with 20/20.

If I were entering a four year college and understood
THAT statistic correctly, I think I would be interested
in doing something about it.

But that would be a matter of intelligent understanding
of the pilot concerned with keeping his 20/20 vision
for the four years he would be in an aeronautical
college.

That is the point, my friend.

Neither I nor you could ever make that kind of decision
for the man. Just provide him the facts, and
allow him to make a choice for a "fighting chance".

He has nothing to lose -- and it is clear as
to what will happen if he chooses to do nothing.

But you put a different "spin" on these obective
facts concerning the behavior of the natural eye
at a four year military college.

Best,

Otis
Engineer


******


If, as you propose, the use lof lenses changes

 

(Otis Brown) wrote in

A refractive status of zero does not imply "squinting 20/20." What it says
is that the very best visual acuity for this person is achieved with a lens
of zero power. Your premise is wrong.

If a person squints, then they are probably already nearsighted.

Doesn't "fighting chance" imply at least a 50:50 chance of success?

 

(Otis Brown) wrote in message

Dear DrJudy,

I need a copy of this for my records -- and to
present to pilots entering a four year college.

I think they will understand the statistics
presented by Dr. Hayden. If they do not -- then
too bad.

My appreciation that "prevention" with a plus
lens is not easy or "quick", and the pilot
(at 20/30 or 20/40) should spend a
year evaluating your arguments and these
statistics BEFORE he takes any action.

Success favors a prepared mind.

Best,

Otis
Engineer

*****