Snellen and glasses

[Otter]

If you can see the snellen at 20/20 with glasses, could your eyesight be worse and you not know it?  In other words, does diopters change along with distance vision?  Sry its just hard for me to explain this.

[Otter]

wait i know how to explain it now.  Does diopters worsen/improve along with distance vision?

[otis]

Dear Otter,

Let me simplyiy the eye's behavior, and the proven
effect of a -3 diopter lens on all fundamental eyes.

A refractive STATE of zero is considered normal.

So we check to see if a -3 diopter lens is even SAFE,
i.e., does not produce a negative refractive STATE,
or "cause nearsightedness", if you will.

This is a critical scientific experiment, because
the majority-opinion ODs ASSUME the minus has
NO EFFECT.

The scientific TRUTH?

You place a -3 diopter lens on the fundamental
eye, and in less than two months the eye
will change its STATE by -2 diopters. 

Thus, the eye "follows" the minus as a fundamental
principle.

If this were done to a human, the result
would be 20/140 vision, in an eye that
had a refractive STATE of zero to start with.

Thus while the minus "works" and "impresses",
it is a "solution" that creates a secondary-problem.

As Bates pointed out -- and is now proven, you
should see methods to avoid the minus, and
PASS the DMV test.  Thus avoiding the minus.

To me this resolves the issue on a scientific
level.

Otis

[otis]

Dear Otter,

I am not certain how to answer your question.

But keep in mind what is proven about the effect
of a strong minus on the eye's refractive STATE.


Otter>  If you can see the snellen at 20/20 with glasses, could your eyesight be worse and you not know it?

Otis> The normal process is to put up a Snellen, and have
you read at say 20/70, or so.  Minus lenses are placed
in front of your eyes, until one is found to clear the
20/20 line.  You question is not clear to me.


In other words, does diopters change along with distance vision?  Sry its just hard for me to explain this.

Otis>  Your eyes must AUTOMATICALLY change their
power when you look from distance to near.  The
amount of change is directly a result of what
you look at. 

Best,

Otis

[Kazekage]

Does diopters worsen/improve along with distance vision?

Yes, this is called accommodation. I think diopters move in a negative state when seeing objects up close, and in a positive state when seeing distance objects. Accommodation is a mechanism the eye uses to focus at different distances.

Accommodation is the process by which the eye increases optical power to maintain a clear image (focus) on the retina. The principal focusing ability of the (terrestrial) eye is due to the difference in refractive index between air and the curved cornea, but the variable curvature of the lens allows for an additional adjustment. This varies from a maximum of over 15 diopters in an infant to only about 1.5 diopters in a person 70 years old, as the lens becomes less flexible with age.

Some theories about how it works:

- Helmholtz - The most widely held theory of accommodation is that proposed by Hermann von Helmholtz in the middle of the 19th century. When viewing a far object, the circularly arranged ciliary muscle relaxes causing the lens zonules and suspensory ligaments to pull on the lens, flattening it. The source of the tension is the pressure that the vitreous and aqueous humours exert outwards onto the sclera. When viewing a near object, the ciliary muscles contract (resisting the outward pressure on the sclera) causing the lens zonules to slacken which allows the lens to spring back into a thicker, more convex, form.

- Bates - In 1920, William Bates stated in Perfect Sight Without Glasses that the contraction of two extraocular muscles, the superior and inferior obliques, were responsible for accommodation.

-Schachar - Ronald Schachar argues that, in opposition to Helmholtz's theory, the ciliary muscle actually pulls on the crystalline lens' equator in an outwardly radial manner, and the consequent changes in lens shape increase the lens power.Counterintuitive indeed, this pulling reportedly steepens central curvature and flattens peripheral curvature. He goes further to explain that it is not sclerosing or stiffening of the crystalline lens that linearly reduces accommodative amplitude, rather that age-related increase in lens diameter reduces the space between ciliary body and lens, linearly reducing the effectivity of the ciliary body's effect on lens dynamics. The "Scleral Expansion Band" technique for the surgical reversal of presbyopia is based on this theory, however, the efficacy of the procedure has been met with skepticism.

-Catenary - D. Jackson Coleman proposes that the lens, zonule and anterior vitreous comprise a diaphragm between the anterior and vitreous chambers of the eye. [5] Ciliary muscle contraction initiates a pressure gradient between the vitreous and aqueous compartments that support the anterior lens shape in the mechanically reproducible state of a steep radius of curvature in the center of the lens with slight flattening of the peripheral anterior lens, i.e. the shape, in cross section, of a catenary. The anterior capsule and the zonule form a trampoline shape or hammock shaped surface that is totally reproducible depending on the circular dimensions, i.e. the diameter of the ciliary body (Müeller’s muscle). The ciliary body thus directs the shape like the pylons of a suspension bridge, but does not need to support an equatorial traction force to flatten the lens.

- <!-- m --><a class="postlink" href="http://en.wikipedia.org/wiki/Accommodation_%28eye%29">http://en.wikipedia.org/wiki/Accommodation_%28eye%29</a><!-- m -->

So basically no one is exactly sure, the dispute is ongoing... I think it's probably a mixture of Bates and Helmholtz  ??? maybe

[otis]

Dear Otter,

Do not get "lost in the sauce".

Go back to baics.  Bates said that the entire eye "accommodates" -- for
the long-term. 

I think we should concentrate on THAT issue, and not get
"lost" in these detailed "arguments".

As Kaze said, the eye accommodates, and the DETAILS of
HOW it does it, and be left for future experiments.

The main issue is that Bates was right, that you could
clear your Snellen -- if you WORKED AT IT.

You have the elements of success.

Now the difficulties:

1.  Any of these preventive methods are an intrusion in your
life.

2.  This intrusion can not be prescribed.  You must do it
youself.

3.  If you are successful, you will see you Snellen clear
from 20/80 to 20/40 or better.

4.  It will take some time to do it.

But on the positive side, experts like Dr. Jacob Liberman have
done it TO HIMSELF.

And I think that is the real power of Bates.

Otis