The Variability of the Refraction of the Eye

Re: The Variability of the Refraction of the Eye

On 25 Apr, 20:17, "Mike Tyner" <mty...@mindspring,com > wrote:
> "Szczepan Bia³ek" <sz.bia...@wp.pl> wrote
>
> > I was told that the children errors "jumps". Is it truth?
>
> In children, refraction can vary drastically due to accommodation.
>
> The sclera and other anatomical structures do not suddenly grow or shrink.
>
> > We have agreed that the accomodation is automatically started with
> > converging. This is done by parasympathetic nerves. Is it not possible
> > that this nerve system works incorrectly?
>
> Yes. Sometimes the parasympathetic overaction serves a purpose, so we don't
> say "incorrect".
>
> In any event, parasympathetic overaction is not anatomical refractive error.
> It goes by many names - spasm of accommodation, latent hyperopia, tonic
> accommodation, all the same mechanism.
>
> It is the reason children are often given atropine or cyclopentolate before
> measurements are made.
>
> -MT

What causes the parasympathetic overaction?

Re: The Variability of the Refraction of the Eye


"Zetsu" <absolutelyinvincible@hotmail,com > wrote

> What causes the parasympathetic overaction?

It's a normal reflex.

In farsighted people, it maintains focused vision, so the "cause" would be
the activity of a normal reflex loop.

In young people who aren't farsighted, "overaction" isn't very common.

When it does occur, we call it spasm of accommodation, or pseudomyopia.

Sometimes it provides better binocular balance, as in convergence
insufficiency.

Other times there's no measurable benefit and it's actually detrimental to
performance.

In those cases, anxiety is usually the most-cited cause.

Re: The Variability of the Refraction of the Eye

These are all distinguished from the normal half-diopter or so of tonic
accommodation you find in most people. I don't call that "overaction,"
because everybody does it.

-MT

"Mike Tyner" <mtyner@mindspring,com > wrote in message
news:5sSdnZviCN58MInVnZ2dnUVZ_jmdnZ2d@giganews,com ...
>
> "Zetsu" <absolutelyinvincible@hotmail,com > wrote
>
>> What causes the parasympathetic overaction?
>
> It's a normal reflex.
>
> In farsighted people, it maintains focused vision, so the "cause" would be
> the activity of a normal reflex loop.
>
> In young people who aren't farsighted, "overaction" isn't very common.
>
> When it does occur, we call it spasm of accommodation, or pseudomyopia.
>
> Sometimes it provides better binocular balance, as in convergence
> insufficiency.
>
> Other times there's no measurable benefit and it's actually detrimental to
> performance.
>
> In those cases, anxiety is usually the most-cited cause.
>
>
>
>