test

You are forgetting not everyone is correctable to 20/20. Surgeons aim
for 20/20 because its the golden standard of perfect vision. Many
people arent capable of this and a few may be capable of better, such
as 20/15 and occasionally 20/13 or 20/10. Not only that, since all
laser surgury induces more high order aberrations, you may experience a
loss in quality and sometimes also accuracy of vision. I cant tell you
how many people lose one or two lines of BCVA. They never see 20/20
again after lasik.

20/30 to 20/40 is not quite perfect but considering you can be 20/400
or count fingers without glasses, its a very big improvement and will
greatly reduce your dependancy on glasses if not eliminate them.

http://upload.wikimedia.org/wikipedia/de/4/42/Sch%C3%A4rfe_optik.jpg

This looks like the 20/40 I see.

http://upload.wikimedia.org/wikipedia/de/4/42/Sch%C3%A4rfe_optik.jpg

Looks like 20/200 vision to me.

"My question is why do optometrist only try to correct to 20/20 even
though through full correction much higher vision would be possible?"

Optometrists try to correct the best your eyes are capable of. This
means if they are capable of 20/15 then he will get you there. If they
only see 20/40 then thats all you can be corrected to. They first try
to get you to 20/20 because for many people, this is the point where
they achieve plano. Optometrists assume if you dont get to 20/20 you
arent plano yet and keep trying a few times then say thats your BCVA.
Mine tried like 3 or 4 times to get me to 20/20 but I cant correct to
perfect vision and neither can my mother, father nor brother.

"Theoreticaly by seeing 20/20 you can still have an error of i.e. -0.50

to -1.00 dpt. (Which means everything what is further then two to one
meters away gets blurry)."

I would not even call it a blur. Someone whos -1 and seeing 20/10 would
of course be capable of seeing better than 20/20 with correction.
Another person may be plano and see 20/20. Both people at 20/20 will
see equally well from a distance reguardless of pescription. The
exception is lasik 20/20 which may not be the same quality as 20/20
with virgin eyes. I know this lady whos -.75 and sees 20/20 without
glasses, 20/15 with glasses and says the difference is very very small.
Shes upset she got pescribed glasses and was told to wear them. Shes
seeing an ophthamologist for a 2nd opinion and in the meantime shes
been going much of the time without glasses.

"When correcting this, glasses would boost you up to a visus of 1.6
(20/13)."

Then you can wear glasses on occasion but they are highly optional if
you meet the DVM of 20/40(and especially if you exceed it)

"20/40 would be equal seeing things at 50%!?! I don't know how it is
with
you, but seeing objects with 50% wouldn't satisfy me. And i think no
matter which situation (extreme or common) you should always have the
best vision possible."

If a person sees 20/40, at 20 feet from the chart that person can read
letters that a person with 20/20 vision could read from 40 feet away.
The 20/40 letters are twice the size of 20/20 letters; however, it does
not mean 50% vision since 20/20 sounds like it is one half of 20/40. If
20/20 is considered 100% visual effiency, 20/40 visual acuity is 85%
efficient.

My comments: While 20/40 is half the visual acuity of 20/20, its 85% as
functional or efficient as 20/20. People who see 20/40 are quite
functional despite half the acuity. If you are already wearing glasses
and they are too weak, get stronger glasses. But if you arent wearing
them, you dont have to if your not having trouble seeing. I know tons
of friends with a -1 pescription and some with even -2 and they go
without glasses. Why? you ask? They dislike glasses, simple as that.

"Of course he can see anything he wants... For example he would see a
car. He would know it is a car because it moves and has four black
things which your brain tells him that are wheels. BUT he couldn't see
which brand it is or what the driver looks like. He couldn't make a
difference if the car has a silver or light blue painting."

He could see everything including what the driver looks like. He can
see the color of the car, heck even I can without glasses and im 20/400
without. of course he does wear glasses to drive, but even that he
doesnt have to but does it for good measure. 20/70 is legal to drive
here so he isnt restricted because hes 20/60. He chooses to wear
glasses for driving, nothing wrong with that when it comes to safety
but for anything else, he doesnt wear glasses.

By the way, whats your pescription and how well do you see with and
without glasses? My pescription is below:

left eye: -4.5 sphere, -.75 cylindar(140 axis) correctable to 20/30
right eye: -3.5 sphere, -1.5 cylindar(55 axis) correctable to 20/40

Dear Chris,

Subject:  Does a minus lens have an "effect" on the refractive
state of the natural eye.

Re:  #1  Dynamic concept -- proven with the primate eye -- YES!

Re:  #2  Box-camera (frozen eye) concept -- not proven, but assumed --
NO!

There are two schools of "though" about the natural eye's behavior
as described above.

The reason you whould NOT go for a strong minud (creating
20/10 in a 20/30 eye) is because of the concern that
that minus will (as a secondary effect) create stair-case myopia,
and the cynamic eye controls its refractive state to BOTH
a "confined" environment with that environment made even
more "confined" by the minus lens.

But it is very difficult to resist the urge to give the person
very, very sharp vision as you state.

There is repeated "Gnashing of teeth" over this issue
as you might have understood from reading some of these
posts.

There is NO RESOLUTION to this issue, so "practice" becomes
the "majority opinion" (Theory number 2) and the second-opinion,
concept number 1.

There are good reasons (in young children) to be very "careful"
with that minus.  See:

www.chinamyopia.org

for this second-opinion.

As always, enjoy our pleasant analytical discussions
about the natural eye's proven behavior as a matter
of fundamental science.

Best,

Otis

++++++++++++++++++

20/20 is normal.  It is better to have normal vision than worse vision.  
No informed person here would claim that 20/20 is the best.

I believe it is more of a language problem.  I have never had a
refraction where an OD stopped trying to get better vision at 20/20.  No
OD on this group says that they do this, either.

Quoting what aceman says will not make you friends on this group.  He is
trying very hard to learn as much as he can about vision, but many of
his posts are far from correct.

20/20 simply means that you see at 20 feet what a normal person sees at
20 feet.  20/30  means that you see at 20 feet what a normal person
could see at 30 feet.  20/15 means you can see at 20 feet what a normal
person can only see at 15 feet.  In all three cases, the measurement is
taken at 20 feet, and says nothing at all about what you can see at one
or two meters.  Despite the conversion chart published on this group by
aceman, converting Snellen results to diopters, it doesn't always work
that way.  

Is this your actual experience, or just based on what the wackos on this
group have posted?

As far as refractive surgery goes,  there are reasons to undercorrect
myopes.

Optometrists always try to give the best vision possible, whether it's
20/20, 20/15 or 20/30. Or whatever. And patients love it if you can get
them to a good 20/15 instead of plain old 20/20.

Some patients who are say 20/30 uncorrected might be quite happy to live
with that and avoid glasses, and that's fine. But others want the best
possible vision - different individuals have different expectations.
What is acceptable to one individual (e.g. Aceman) may be seen as
entirely unacceptable to another. People are different.

Refractive surgeons don't aim for an acuity (e.g. 20/20), they aim for a
refraction (e.g. 0.00 or -0.75). If they subsequently achieve 20/20 then
they are satisfied. 20/15 would be a bonus.

Dom

Dear Chris,

The term "20/20" is more akin to a metaphor for the BCVA, which is the
"best corrected visual acuity."  For most people, the BCVA is 20/20 or
1.0 decimal, for some it is 20/15 or 1.3 decimal, and still fewer can
go to 2.0 or 20/10.

Someone here really messed up the forums by providing some fault
information.  Obviously the people in the know are quite frustrate
it and I'm having trouble comprehending when there's exces
information about metaphors and semantics.

I'll start by trying to answer the actual question

20/20 was determined when the eye is at it's relaxed state, starin
into the distance that an object should focus to a point on the bac
of the eye.  This optimal distance was decided at 20 feet.  So
measurement of how clear or unclear a person's visual acuity is no
measured by 20/20.  You see at 20 feet what you SHOULD be seeing a
20 feet.

Some people's eyes are capable of seeing things at 20 feet what th
norm should be seeing at 15 feet.  So you see better!.. and som
people eyes are not as good because of one reason or another and the
see 20/30.. so you see something sharp at 20 feet when others see i
at 30 feet.

A lens put in front of your eye, being contact lens or eyeglasses wil
"BEND" the light accordingly so that the light focuses where i
should.  With people who are far sighted, the image focuses past th
point where it should.  People who are near sighted, the imag
focuses before the point where it should.  LENSES, help push thi
focus point to where it should be for the best vision possible

Some people can deal with 20/30 sight because most of their lifestyl
maybe more critical for near vision .. and less for far vision.  Tha
is why some people don't mind it even though it's less than optimal.

Optometrists or Ophthalmologists will try to correct for 20/20 .. i
you can see better than that, then they will correct for it.. bu
most people don't need it.  Even if you put a higher prescription i
front of someone's eye will not make it sharper for them.. it wil
most likely make their eyes more tired by the end of the day.

Hopefully that explains things

FURTHERMORE, Chris a plus lens... +2.00D does not make things smaller
A +2.00 lens is basically a magnifying lens and therefore will mak
objects look larger.

If refractive error is exactly neutralized, you get the best you can get. If
you don't have the best you can get, either the corrective lens is too
strong or it isn't strong enough.

In this case (for myopia), I would prefer a lens that isn't quite strong
enough, since this at least makes reading more comfortable. If it's too
much minus, that doesn't help for any task.