correcting vision better than 20/20

[Bucky]

Can vision be safely corrected better than 20/20? I'm guessing there
must be tradeoffs of correcting vision with glasses, contacts, or laser
beyond 20/20.

[o***@pa.net]

Dear Bucky,

Subject: The "standard" 20/20.

Most people (no medical condition -- and young), will
have visual resolution of 1 minute-of-angle, or be
able to read 3/8 inch letters at 20 feet.

A number of people can have vision sharper than
20/20, with the use of a stronger minus lens.

Some ODs use this as a standard to prescribing
a minus lens, and this is called prescribing
for "Best Visual Acuity".

Most DMV tests require 20/40 with both
eyes, or 20/40 in the better eye, with no
lens.

Post by Bucky
Can vision be safely corrected better than 20/20?

Otis> That is a "loaded" question. It depends on exactly
what you mean by "safely". Ther are those who
suggest that a strong minus lens accellerates
the development of nearsightedness. The
"jury" is still out on that subject. Some ODs
call the minus, "poision glasses for children."


I'm guessing there

Post by Bucky
must be tradeoffs of correcting vision with glasses, contacts, or laser
beyond 20/20.

Otis> That is a judgment you will have to make for yourself.

Best,

Otis

[Mike Tyner]

Post by o***@pa.net
A number of people can have vision sharper than
20/20, with the use of a stronger minus lens.

Except for those who see better with a stronger _plus_ lens, or a stronger
_cylinder_ lens. The majority of people in the US are not nearsighted.

Post by o***@pa.net
Some ODs use this as a standard to prescribing
a minus lens, and this is called prescribing
for "Best Visual Acuity".

Of course hyperopes have no BVA, and it's only the OD's who use this
standard.

Post by o***@pa.net
Most DMV tests require 20/40 with both
eyes, or 20/40 in the better eye, with no
lens.

Of course nobody needs to see better than 20/40. Anything better than 20/40
is harmful to the eye.

You might as well killfile me again, Mark. I see clouds puckerin' up to come
a-squirt.

-MT

[Neil Brooks]

Post by o***@pa.net
Dear Bucky,
Subject: The "standard" 20/20.
Most people (no medical condition -- and young), will
have visual resolution of 1 minute-of-angle, or be
able to read 3/8 inch letters at 20 feet.
A number of people can have vision sharper than
20/20, with the use of a stronger minus lens.
Some ODs use this as a standard to prescribing
a minus lens, and this is called prescribing
for "Best Visual Acuity".
Most DMV tests require 20/40 with both
eyes, or 20/40 in the better eye, with no
lens.

Post by Bucky
Can vision be safely corrected better than 20/20?

Otis> That is a "loaded" question. It depends on exactly
what you mean by "safely". Ther are those who
suggest that a strong minus lens accellerates
the development of nearsightedness. The
"jury" is still out on that subject. Some ODs
call the minus, "poision glasses for children."
I'm guessing there

Post by Bucky
must be tradeoffs of correcting vision with glasses, contacts, or laser
beyond 20/20.

Otis> That is a judgment you will have to make for yourself.
Best,
Otis

This is all very interesting, Otis. WITHOUT pointing to any point of
your own anatomy, could you kindly cite your source for this
information?

Thanks.

[William Stacy, O.D.]

Post by o***@pa.net
A number of people can have vision sharper than
20/20, with the use of a stronger minus lens.

As Regan once said, "There you go again!".

In fact, the vast majority of humans can see better than 20/20. Some do
so with a little plus. Some with a lot of plus. Some with some cyl.
Some with a zero power rigid contact lens. Some with no lens at all (in
fact MOST humans in the world fall into this category). And yes, some
do so with minus lenses. Some with WEAKER minus lenses, some with
moderate power minus, and yes, a few do so with strong power minus. So
what? Get over it.

w.stacy, o.d.

[Bucky]

Post by o***@pa.net
That is a "loaded" question. It depends on exactly
what you mean by "safely". Ther are those who
suggest that a strong minus lens accellerates
the development of nearsightedness.

OK, I'm not talking about long term safety. I just mean "safely"
meaning you can wear that correction all day without getting a
headache. Can a typical nearsighted person be corrected to 20/5 or
20/1, or what's the limit?

[Dan Abel]

Post by Bucky
Can vision be safely corrected better than 20/20? I'm guessing there
must be tradeoffs of correcting vision with glasses, contacts, or laser
beyond 20/20.

20/20 simply means that you see at 20 feet what a "normal" person sees
at 20 feet.

The goal in correcting vision is to give you the best possible, not some
arbitrary number.

[Bucky]

Post by Dan Abel
The goal in correcting vision is to give you the best possible, not some
arbitrary number.

So why not attempt to correct nearsighted people's vision to 20/5 or
20/1? Isn't that better than 20/20?

[Mike Tyner]

Post by Bucky
So why not attempt to correct nearsighted people's vision to 20/5 or
20/1? Isn't that better than 20/20?

Because there's a limit to how many photoreceptors you have in your retina.

If you focus a camera perfectly - not behind the object, not in front of the
object, but exactly on the object, then the film is what limits the
resolution of the photo.

-MT

[Bucky]

Post by Mike Tyner
If you focus a camera perfectly - not behind the object, not in front of the
object, but exactly on the object, then the film is what limits the
resolution of the photo.

Ahh, thank you, that was a helpful analogy.

How about lenses that also magnify then? Let's say a baseball player
who is 20/20 wants to be 20/10. Could he get lenses that magnify to
achieve that resolution? In this case, I suppose that the tradeoff
would be field of view. But is this possible?

[Mike Tyner]

Post by Bucky
How about lenses that also magnify then? Let's say a baseball player
who is 20/20 wants to be 20/10. Could he get lenses that magnify to
achieve that resolution? In this case, I suppose that the tradeoff
would be field of view. But is this possible?

Of course it's possible, but it may not be practical.

If the baseball player is _farsighted_, it's a simple matter of pushing the
glasses out far enough off his nose to magnify, as you would with a
"magnifying" glass (both are _plus_ lenses.) We call this increasing the
"vertex distance", the distance from the cornea to the back lens surface.
The problem with doing this is 1) you may have to push them too far out to
be practical, and 2) the lens _power_ changes with increases in vertex
distance so the actual prescription must be changed to get the same lens
"effectivity."

OTOH, if the baseball player is _nearsighted_, his normal lenses _reduce_
image size, so there's no manipulation that will make the image _bigger_.
Best you could do is contacts, where the vertex distance is zero, and no
minification occurs.

Both of those options assume you're limited to a single pair of lenses, one
in front of each eye.

If you really want mag, you make a telescope with two lenses over each eye:
a plus lens placed forward to magnify, and a minus lens placed closer to the
eye to correct the focusing error introduced by the plus. With the minus
lenses being closer, they won't minify much, while at greater distance the
plus lenses _will_ magnify and the system is designed to create a net zero
power (or net -1.00 or +3.00, whatever the original prescription might have
been.)

-MT

[o***@pa.net]

Dear Bucky,

Bucky> How about lenses that also magnify then? Let's say a baseball
player

Post by Bucky
who is 20/20 wants to be 20/10. Could he get lenses that magnify to
achieve that resolution? In this case, I suppose that the tradeoff
would be field of view. But is this possible?

Yes, a 4 power telescope will provide that type
of angular magnification -- but not very practical.

Otis

=============

Post by Bucky

Post by Mike Tyner
If you focus a camera perfectly - not behind the object, not in front of the
object, but exactly on the object, then the film is what limits the
resolution of the photo.

Ahh, thank you, that was a helpful analogy.
How about lenses that also magnify then? Let's say a baseball player
who is 20/20 wants to be 20/10. Could he get lenses that magnify to
achieve that resolution? In this case, I suppose that the tradeoff
would be field of view. But is this possible?

[A Lieberma]

Post by o***@pa.net
Dear Bucky,

Dear Bucky,

Please disregard Otis's postings. He is not in the medical profession and
not in any position to give medical advice.

Thanks!

Allen

[William Stacy, O.D.]

Post by o***@pa.net
Dear Bucky,
Bucky> How about lenses that also magnify then? Let's say a baseball
player

Post by Bucky
who is 20/20 wants to be 20/10. Could he get lenses that magnify to
achieve that resolution? In this case, I suppose that the tradeoff
would be field of view. But is this possible?

Yes, a 4 power telescope will provide that type
of angular magnification -- but not very practical.
Otis

Ok otis, now you amaze me. You actually made a statement that makes
sense. I'm dumbfounded. I don't know what to say. If you are that
smart, why then do you keep posting the other nonsense stuff on this
newsgroup?


w.stacy, o.d.

[o***@pa.net]

Ok otis, now you amaze me. You actually made a statement that makes
sense. I'm dumbfounded. I don't know what to say. If you are that
smart, why then do you keep posting the other nonsense stuff on this
newsgroup?

Otis> Thanks!

Otis> And as you might know, I do have friends in both ophthamology
and optometry. But we respect each other. They have been
wonderful.

Best,

Otis


w.stacy, o.d.

Post by William Stacy, O.D.

Post by o***@pa.net
Dear Bucky,
Bucky> How about lenses that also magnify then? Let's say a baseball
player

Post by Bucky
who is 20/20 wants to be 20/10. Could he get lenses that magnify to
achieve that resolution? In this case, I suppose that the tradeoff
would be field of view. But is this possible?

Yes, a 4 power telescope will provide that type
of angular magnification -- but not very practical.
Otis

Ok otis, now you amaze me. You actually made a statement that makes
sense. I'm dumbfounded. I don't know what to say. If you are that
smart, why then do you keep posting the other nonsense stuff on this
newsgroup?
w.stacy, o.d.

[VicTek]

Post by Bucky

Post by Mike Tyner
If you focus a camera perfectly - not behind the object, not in front of the
object, but exactly on the object, then the film is what limits the
resolution of the photo.

Ahh, thank you, that was a helpful analogy.
How about lenses that also magnify then? Let's say a baseball player
who is 20/20 wants to be 20/10. Could he get lenses that magnify to
achieve that resolution? In this case, I suppose that the tradeoff
would be field of view. But is this possible?

In other words, could a baseball player play well wearing binoculars? <g>

[Mike Ruskai]

On or about 30 Nov 2006 23:46:57 -0800 did "Bucky"

Post by Bucky

Post by Dan Abel
The goal in correcting vision is to give you the best possible, not some
arbitrary number.

So why not attempt to correct nearsighted people's vision to 20/5 or
20/1? Isn't that better than 20/20?

There are two factors affecting visual acuity - optical aberrations
and retinal density.

20/20 is what's expected of a person with baseline optical aberrations
and normal retinal density.

I don't know off hand what a normal retina could do with the best
possible correction of optical aberrations (which cannot be removed
entirely - perfect optics cannot exist, due to the wavelike properties
of light), but it certainly won't be 20/5, let alone 20/1.

If you want that kind of "correction", you want a bionic eye.

[o***@pa.net]

Post by Bucky

Post by Dan Abel
The goal in correcting vision is to give you the best possible, not some
arbitrary number.

So why not attempt to correct nearsighted people's vision to 20/5 or
20/1? Isn't that better than 20/20?

Yes it is, but the AVERAGE of a population was measured
and established to be about 1 minute-of-arc resolution.

Or the AVERAGE person could be "corrected" to 20/20,
or reading 0.9 cm letters at 6 meters.

Obviously, some can do better, and some can not
read this size letters.

In recognition of this fact, the DMV departments had
set their standard as reading 1.8 cm letters at 6 meters.

Because some people can not even be "corrected"
to 20/20.

Best,

Otis

[VicTek]

Post by Bucky

Post by Dan Abel
The goal in correcting vision is to give you the best possible, not some
arbitrary number.

So why not attempt to correct nearsighted people's vision to 20/5 or
20/1? Isn't that better than 20/20?

In my experience when the lens was made stronger (beyond optimal) the acuity
didn't improve. I just experienced discomfort and realized I needed a
better optometrist.

[odtobe]

To those that may care recent research has determined that if use the
photoreceptor density in the fovea, part of the eye that gives most
detailed vision in normal eyes, the estimate for acuity is around 20/8,
believe it or not. Now that is not the entire story, the light gets
scattered/reflected/lost a little bit while traveling through the eye
detracting from this 20/8 possibility.

I can see 20/15+ with both eyes, corrected with toric soft contact
lenses, anything less and I go nuts. However, not everyone
needs/appreciates better acuity, but most are happy with 20/20. The
reason for the 20/20 can have a lot to due with leading an exam, if
20/20 acuity or better is met you can rule out a lot of pathology or
additional problem, if 20/20 is not met investigation as to why is
necessary.

Sorry to be long winded.
ODTOBE

Post by VicTek

Post by Bucky

Post by Dan Abel
The goal in correcting vision is to give you the best possible, not some
arbitrary number.

So why not attempt to correct nearsighted people's vision to 20/5 or
20/1? Isn't that better than 20/20?

In my experience when the lens was made stronger (beyond optimal) the acuity
didn't improve. I just experienced discomfort and realized I needed a
better optometrist.

[Dan Abel]

Post by odtobe
I can see 20/15+ with both eyes, corrected with toric soft contact
lenses, anything less and I go nuts. However, not everyone
needs/appreciates better acuity, but most are happy with 20/20.

They better be happy. By definition, 20/20 is "normal" vision.

[David Combs]

Post by odtobe
However, not everyone
needs/appreciates better acuity,

For absolute proof of that, just look at people's
eyeglasses -- how clean/dirty they are!

(Likewise, check out their cars' windshields -- same
thing!)


David