Flitcroft paper on "stair-case" change in refractive status

To: Friends

From: Otis Brown

Subject: Vision paper on myopia "staircase" effect.

Here is the paper that shows the "stair-case" response
Of the natural eye to:

1. A confined visual environment.

2. The effect of a series of increasingly stronger minus lenses,
to match the "induced" negative refractive status.

3. The result is that the "step input" is the minus lens,
and the response is exponetial (e ^ -t/Tau) "cusps", which is the
response you would expect from an automatically focused
camera that gains its "input" from the accommodation SIGNAL.


Best,

Otis

*****

Pergamon -- Vision Research

Vision Research 38 (1998) 2869-2879


Flitcroft Vision

A model of the contribution of oculomotor and optical factors
to emmetropization and myopia.

D. I. Flitcroft

Institute of Ophthalmology, University College Dublin 60
Eccles Street, Dublin 7, Ireland

Received in revised form 15 December 15, 1997

Abstract:

The purpose of this work was to investigate quantitatively
the interactions between accommodation, vengeance and a mechanism
of emmetropization driven by optical blur within the retinal image
with a view to developing a model that provides an explanation of
both normal emmetropization and near-work associated myopia. The
simulations of the change in the refractive state of the eye over
time that derive from this model indicate that optical regulation
of eye-growth can result in emmetropization, i.e., a progressive
reduction in refractive errors over time leading towards
emmetropia.

This occurs when viewing conditions involve a preponderance
of distance work. With increasing near work, the model predicts
that the refraction of the eye will converge towards myopia. In
keeping with the previously reported associations of myopia with
esophoria, poor accommodation function and high AC/A ratios, these
conditions increase the amount of myopia produced under intensive
near viewing conditions but do not lead to myopia during mainly
distance viewing.

The model provides quantitative validation of the hypothesis
that the epidemiological association between myopia and increased
near-work may be caused by a disturbance of normal emmetropization
by steady state errors of accommodation.

The same model can explain normal emmetropization, increasing
myopia with increasing near-work demands and the currently
recognized oculomotor associations that have been reported to
precede the development of myopia.

Elsevier Science Ltd.


Keywords Accommodation, Vengeance; Myopia; Emmetropization

___________

The paper is covers 11 pages.

I received it from Dr. Dave Guyton at JHU.

_____________

Figure 9

Graph showing the change in refractive (vertical axis) over
repeated interactions (horizontal axis) from a starting refraction
of +2 D with other parameters as for Fig 4a. The dotted line
shows the change in refraction without spectacle correction and
the dashed line shows the effect of progressive correction of the
induced myopia (spectacle correction shown as solid line).

Figure 10

Graph showing the change in refraction (vertical axis) from a
starting refraction of +2 D with other parameters as for Fig. 4a.
The dashed line shows the change in refraction with a -0.5 D
correction from iteration 20. The dotted line shows the effect of
a -0.5 D distance correction with a +1.5 near addition.

 

I'm glad that Otis brings up Flitcroft. You will also notice that he
selectively quotes from a paper published in 1997.

I would now like to quote from a paper published in 2004, by RA Stone and
DI Flitcroft, entitled Ocular Shape and Myopia (Ann. Acad. Med. Singapore,
vol. 33):

"The insight that normal refractive development is regulated by visual
quality has diminished the likelihood that accommodation comprises a
primary mechanism for the cause of myopia... Bifocal and varifocal lens
treatments, at least with protocols adapted to date, have either revealed
NO reduction of myopia progression OR a stasticially significant reduction
that is too small in magnitude for clinical import."

You see, friends, even Flitcroft recognizes that new scientific information
requires a re-adjustment in one's thinking.

DrG


(Otis Brown) wrote in

 

Excellent! That is one helluva "got you" there!

You see, folks, the difference between SCIENTIST and ZEALOT is indeed
clear. Otis, now matter how many times he is shown *science* will retort
with the typical "zealot response": "stop confusing the issue with the
facts! I know what it true because I understand the *true* workings of
the system."

And then: "There's a conspiracy to support the wrong conclusions."
And then: selectively chosen, often ancient (but since
adjusted/corrected) reprints, often out of context, in the continuing
struggle to support unsupportable claims.

The definition of a zealot.

Go, Otis. Go. Show us more BS. Or better still, just go away.

--LB

 

Wow! I hadn't realized Otis was advocating bifocal and varifocal lens
treatments to restore unaided distance acuity. Thanks for the
clarification!

I assume by your quoting Flitcroft's 2004 article that you believe "normal
refractive development is regulated by visual quality". I didn't get
further than the abstract on PubMed, so I will trust your presentation is
from the body of the article and is not out of context. So, what is
providing the visual quality? From further in your quote, it would seem to
be bifocals. Therefore, the bifocals are regulating normal refractive
development. The outcome of "NO reduction of myopia progression" should
have been predicted precisely because of the control taken by the bifocals
for distance viewing, near work not being the issue in myopia. A second
point I note is that visual quality is suspected, by insight, to push
accommodation out of first place as a "mechanism for the cause of myopia".
Leaving it, potentially, as a secondary mechanism?

The "new scientific information" described in the abstract was that RA Stone
and DI Flitcroft are interested in "incorporating the 3-dimensional
conformation of the eye into future clinical studies". They gave no hint
that they've changed their minds about their 1997 conclusions. Is the
abstract off-base as to the thrust of the paper? Your reply will help me
decide the usefulness of PubMed.

Thanks,

Cathy

 

I quoted from the text of the full article. And, yes, Otis is (in)famous
for promoting plus lenses for the prevention of myopia, and often quotes
studies involving progressive lenses, accommodation, minus lens-induced
myopia in order to promote his theories.

As to the rest of your questions, I will deflect the intellectual energy
for answering them back into your court.

DrG

 

Cathy, let me add one more comment.

I am not saying the Flitcroft changed his position entirely, because his
earlier assertions were quite specific regarding AC/A ratio and nearpoint
esophoria, which Otis ignores entirely. IMHO, Flitcroft left lots of
wiggle room with respect to myopiagenesis, and I think he was trying to
spread his theories too thinly over too much data. The "bandpass" idea
does leave room for a "visual quality" etiology, which the latter paper
advances.

DrG

 

Bifocals for myopes are not plus lenses. They are minus for distance and
less minus for near work. -4.00 +1.75 = -2.25, a net minus. One can't
credibly say plus lenses don't work when the studies that have been cited
used less minus.


and often quotes

As does Flitcroft.

 

Dear Cathy,

Subject: Assumptions you have made about the Flitcroft
paper and interpertations.


The ODs on this site asked me to post a paper discussing
the effect the minus lens has on the refractive status
of the natural eye.

That is the reason I posted the paper -- not that I
agree with the WORDING used in the paper.

I simply state that a sophisticated auto-focused camera
that controls its refractive status to the ACCOMMODATION
SIGNAL, will evince a "stair-case" change if a minus lens
is placed on this auto-focused camera.

From a "cybernetic" point of view, this is what you would
expect from a competent control system. It is a matter
of "jumping the gun" to call refarctive states you don't
like "defects" and the like.

This perspective is called a "paradigm" in fundmental
science. The two paradigms are a "box camera" model
developed from "standard practice", and of course
a cybernetic model -- that respects the design
of this physiological control system.

Some additional commentary.

Cathy -- I do not advocate this approach. I advocate that a
person be informed of the POSSIBILITY of using the plus
at the 20/40 level (still passes the Snellen-DMV line) BEFORE
he (a pilot) begins using a minus lens. This would elliminate
any "bi-focal" or vari-focal lens -- and place the decision
and "control" in the person himself.


Cathy > Thanks for the clarification!

No I do not. I believe that the natural eye controls its
refractive status to the accommodation signal -- which
is a reasonable expectation.


I didn't get

Otis> I quoted the part of the paper showing the "step" produced
by the minus lens and the ( e ^ -t/Tau ) response. I simply do
not have a scanner, and only posted the part of the paper
discussing the effect of repeated increases in minus lens
strength would have on the refractive state of the natural eye.

So, what is

Cathy, pleas read my paper on "A cybernetic model of accommodation".

As long as the lens is within the "stop-to-stop" movement
of the lens -- the image on the retina is perfectly clear.
Excellent quality.

From further in your quote, it would seem to

Otis> If you read my site, you would undertand NO BI-FOCALS.
The goal is to have the pilot clear his distant vision
BEFORE there is a requirement that he wear a minus lens
AT ALL. He must understand this personable responsibility
and take it seriously.


Therefore, the bifocals are regulating normal refractive

Otis> The natural eye will change it refractive state
in a negative direction if you place a minus lens
on it (primate eyes).

The outcome of "NO reduction of myopia progression" should

Otis> That is a matter of strong disagreemen. I depends
on WHO ran the study. I do agree that once you begin
wearing a minus lens -- you will not be able to
clear by use of a plus lens.

A second

Otis> I never said anything about "defect". In the first stage
where the refractive status is -1/2 diopter (20/40) I would
expect that by drastic change of the near enviroment with
a plus lens (changing the average visual enviroment) will
result in the pilot verifing that he can personally
see his distant vision VERY SLOWLY CLEARING back to
20/20 -- and a positive refractive status of some degree.
I have posted reports of pilots who have already done
this on my site. Believe it or not.

They need to apply for further funding for this work -- and
the application must "please" the ophthalmology department.
Yes, I understand this process.


They gave no hint

Otis> You can and will arrive at you own conclusions on that question.


Your reply will help me

Otis> The most important quality you have is your ability
to look at conflicting ideas -- review what you believe
is the "correct" experimental data -- and draw
you own conclusions.

Best,

Otis
Engineer

 

Cathy

I have sometimes worn plus lenses over the top of my distance minus
lenses to do prolonged periods of close work. This kind of plus
lens use was advocated by James Arthur
http://members.aol.com/myopiaprev/improvin.htm who for years was
trying to remove his myopia. He finally concluded that beyond a 1.5D
improvement he was never going to get more improvement. So must of
us would consider varifocal lenses to be plus lens therapy.

However this is all a distraction for me, I dont believe that myopia
has got much at all to do with glasses.

You began your posts to Dr Leukoma with an apparently triumphant
celibration that finally you could now understand what Otis was
talking about.

As wacky as it might seem, I believe that this kind of indirect
communication is related to being myopic.

In myopia there can be a tendency to publicly be a wee bit aggressive
towards others, while actually privately being rather timid or shy.

Visually, in myopia, our focus of attention is close to ourselves.

Myopia seems to arise after stressful experiences in our lives, often
happening at times in our lives when we are vulnerable and have little
control or power to change things around us.

Rather than the environment changing, we changed.

Unfortunately to improve myopia it is not the visual environment that
now has to change!

:-(

Andrew

 

http://www.eyecareforyou.com/ECFYEyeAlignment.htm

?

 

Twice the blur at 20 feet and none at 13 inches.

But accommodation is associated with myopia. Less minus doesn't break the
association. Zero or plus does.


but to apply "plus" equally to people of

 

Accommodation is associated with close work. The purpose of posting
references to Flitcroft and others was to show how the association between
accommodation and myopia may not be as significant as once thought.

DrG

 

Not as significant as the "primary mechanism for the cause of myopia"
because they're thinking image quality regulates eye size and shape which, I
humbly submit, the lens has to accommodate for at all distances. Does that
work? Not being the cause doesn't eliminate it as big trouble.

Don't worry, I'm reading through the magazine. I don't want to miss
anything.

Cathy

 

Otis, may I ask......

This concerns ONE eye of an adult for simplicity reasons..

Can we agree such a sophisticated auto-focused camera has a certain focal
length when the lens is adjusted for infinite?
Can we agree such a focal length has an according power in diopters?
Can we agree putting a minus lens in front is causing a change in the total
refracting power of the unit cameralens + minuslens?
Can we agree the total power of this system (cameralens+minuslens) is lesser
plus?
Can we agree the cameralens has to be moved further from the receiving
(film) plane in this situation ore has to become more plus when wanting a
sharp image?
Can we agree this more pluspower can be controlled by a sophisticated system
and the addition should stop at the moment the control mechanism says
"sharp" ?
Can we agree taking away the minuslens causes the sophisticated control
mechanism to "look" in which direction the sharp image disappeared, forwards
or backwards and go back to the correct focal distance?

Then please recognize a "negative feedback mechanism" in both the eye and
the camera, NOT the positive one you wanted people here to believe.

Jan (normally Dutch spoken)

 

I suspect you are lost in the maze of imprecise knowledge and imprecise
definitions. Please keep reading.

DrG

 

Most studies cite greater myopic progression in children with greater lag
of accommodation, which is associated with higher AC/A ratio, and greater
convergence - i.e. esophoria. The COMET study reported a small, but
significant effect of progressive addition lenses in these patients. It is
as though in order to maintain single binocular vision, the patient has to
give up accommodation, which leads to increased retinal blur.

However, as the Stone/Flitcroft paper says, there are other causes of
retinal blur, such as spherical aberration and coma, which are due to the
shape factor of the eye. This could be one reason why plus lenses are only
minimally effective at best.

DrG

 

.... where I found you. I'll take this as a cordial "Welcome to my world."
and politely reply, "Thank you."

Cathy

 

Dear Dr L,

You keep on "putting words in my mouth" that I have
never said, and ASSUMING many things about me
that simply are not true.

I am well aware of the "Accommodation-Convergence/Accommodation
ratio -- but it is not particularaly relevlant as to
the focal control actions of the natural eye.

The design of the AC/A ratio is discussed effectively
by John Semmlow and Georg Hung in their published
papers.


Best,

Otis
Engineer

Otis> Please read the above remarks.

IMHO, Flitcroft left lots of

 

Francine,

In case this post wasn't merely a test of Mike's forthrightness, he gave
this answer in the lens/distance thread: "One over distance in meters".

Cathy

 

Sorry, I should have continued ...

From there it's just math. Without glasses, a -6.00 myope can focus at
approximately 6.5". 1/(6.5/39.4) = 6.00. At what distance does your myope
want to focus through the weaker part of his bifocals? Plug in your number
for the net minus needed required for that distance. If 14.25",
1/(14.25/39.4) = 2.75. To get from -6.00 to -2.75 you add 3.25. Any weaker
than a net -2.75, and your -6.00 myope will be able to see farther through
the weaker part of the bifocals, but will be accommodating more (possibly an
imprecise term) to focus at 14.25". Of course, when he can't see anything
farther than 14.25" through the -2.75 part, he'll use the -6.00 part and
accommodate as necessary at the intermediate distances.

Cathy