Why is ONLY 20/20 Vision so important?

Discussion in 'Eye-Care' started by Christopher Zoettl, Feb 1, 2006.

  1. I have been watching this newsgroup for sometime and always seen quotes
    that "20/20 vision" is THE best to have. Here in Europe we use a "visus
    table". I'll point out:

    20/70 = aprox. Visus of 0.28
    20/60 = aprox. Visus of 0.3
    20/40 = Visus of 0.5
    20/20 = Visus of 1.0
    20/15 = aprox. Visus of 1.3
    20/13 = aprox. Visus of 1.6

    My question is why do optometrist only try to correct to 20/20 even
    though through full correction much higher vision would be possible?
    In europe it is very common to prescribe full correction to maximize
    vision. I would like to debate this with the following example:

    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).
    When correcting this, glasses would boost you up to a visus of 1.6 (20/13).
    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.
    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. You loose all
    the details (see http://de.wikipedia.org/wiki/Bild:Schärfe_optik.jpg)
    -----------------------------------

    So why do people think seeing things with 20/30, 20/40 is enough? Why do
    refractie surgeons only aim for 20/20 or 20/30 even though the patients
    could have much better vision with conatacts or glases?
    Maybe something to consider...

    Best regards

    Chris
     
    Christopher Zoettl, Feb 1, 2006
    #1
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  2. Christopher Zoettl

    John Guest

    test
     
    John, Feb 1, 2006
    #2
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  3. Christopher Zoettl

    acemanvx Guest

    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/Schärfe_optik.jpg

    This looks like the 20/40 I see.

    http://upload.wikimedia.org/wikipedia/de/4/42/Schärfe_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
     
    acemanvx, Feb 1, 2006
    #3
  4. Christopher Zoettl

    otisbrown Guest

    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

    ++++++++++++++++++
     
    otisbrown, Feb 1, 2006
    #4
  5. Christopher Zoettl

    Neil Brooks Guest

    Aw, crap. I didn't study ;-)
     
    Neil Brooks, Feb 1, 2006
    #5
  6. Christopher Zoettl

    otisbrown Guest

    Dear Quick,

    Please add the words

    "Paradigm"

    "Semantics"

    "Refractive state" not Refractive "error",

    "Paradigm-shift"

    "Second-opinion"

    "Informed choice"

    Best,

    Otis
     
    otisbrown, Feb 1, 2006
    #6
  7. Christopher Zoettl

    Dan Abel Guest

    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.
     
    Dan Abel, Feb 1, 2006
    #7
  8. Christopher Zoettl

    Dom Guest

    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
     
    Dom, Feb 2, 2006
    #8
  9. Ah bummer... What a refreshing change, nothing changed on this NG... :)
     
    Yasar, Mehmet C PFC B Co 602d ASB, Feb 3, 2006
    #9
  10. Christopher Zoettl

    Dr. Leukoma Guest

    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.
     
    Dr. Leukoma, Feb 3, 2006
    #10
  11. Christopher Zoettl

    otisbrown Guest

    Dear Chris,

    The definition of 20/20, was established
    by a Dr. Snellen. It is not a "metaphore".

    It means that you can read characters
    that subtend 5 minutes-of-arc at 20 feet.
    No more, not less.

    There are two defintions of "passing"
    the 20/20 line. They are

    1. You read 1/2 the letters correctly -- the
    DMV

    2. You read 4 out of 5 -- the military.

    Thus 20/20 is 3/8 inch letters and 20/40 is 3/4 inch letters.

    Metric is 0.9 mm and 1.8 mm at 6 meters.

    That is measurement in engineering terms. I do not know how DrG
    converts objective measurements into a metaphore.

    Best,

    Otis
     
    otisbrown, Feb 3, 2006
    #11
  12. Christopher Zoettl

    Dr. Leukoma Guest

    The term 20/20 does indeed have both a scientific, as well as a
    non-scientific meaning. In scientific terms, it is the size of a
    letter subtending 5 minutes of arc at any distance, and not just 20
    feet, mind you. Of course, the test distance will determine the SIZE
    of the letter required to subtend 5 minutes of arc.

    In common use, i.e. lay terms, 20/20 is often used to express the BCVA,
    as most people consider that 20/20 is the best possible resolution.

    Otis, you should quite while you are ahead.

    DrG
    http://coppellfamilyeyecare.com
     
    Dr. Leukoma, Feb 3, 2006
    #12
  13. Christopher Zoettl

    Quick Guest

    wrote:

    This is it folks... the grand prize winner!
    Think about that. Putting quotes around metaphore...

    -Quick
     
    Quick, Feb 3, 2006
    #13
  14. Christopher Zoettl

    otisbrown Guest

    Dear Quick,

    A metaphore, is making a statement like, The ship "ploughed" the sea.
    THAT is a metaphore.

    I do not agree with DrG's use of the word to describe an objective
    chart, and the reading of that chart (1/2 the letters). That is
    objective --
    not a "metaphore".

    The issue is one of sematics -- as the basis of a scientific
    argument about scientific proof. (A subject we should
    discuss at some future time.)

    Best,

    Otis
     
    otisbrown, Feb 3, 2006
    #14
  15. Dear Otis,

    please look at this link and answer me the following questions:

    http://www.usherbrooke.ca/ophtalmologie/images/Predoc/Erreurs_refraction/myopie.jpg

    As you might know a fully corrected or emmotropic eye the light beams
    come to a stop in the fovea centralis. So why should a plus lens or no
    lens at all help? You would even get more blurry vision. How would it
    prevent an eye from getting stair case myopia?

    Best regards

    Chris
     
    Christopher Zöttl, Feb 3, 2006
    #15
  16. Christopher Zoettl

    Dr. Leukoma Guest

    The very same person who regularly turns the medical dictionary on its
    head would defend the correct usage. That's called irony.

    DrG
     
    Dr. Leukoma, Feb 3, 2006
    #16
  17. Christopher Zoettl

    drfrank21 Guest

    Otis, try spelling metaphor correctly in order to gain more
    credibility. Hey, if you're
    going to be nitpicking on grammatical issues at least spell the word
    correctly.
    I guess everybody but you understood what Dr.G meant (metaphor is
    actually a type
    of analogy).

    How about an implicit metaphor for you. "Shut your trap!" qualifies
    and
    sure seems appropriate to me in this case.

    frank
     
    drfrank21, Feb 3, 2006
    #17
  18. Christopher Zoettl

    otisbrown Guest

    Dear Chris,

    Subject: The dynamic nature of the living eye.

    Re: Picture of a "box-camera" use to represent the (presumed)
    living eye.

    Scientific research proves that the living eye changes its
    refractive state (in a negative direction) when you place
    a minus lens on it. What this proves that the living eye
    is a highly-accurate auto-focused camera. (Refractive state is
    measured
    with "classical" atropine. Refractive state can be plus or minus,
    and the living eye completely normal. Refractive states IN THE WILD
    run from zero to +2 diopters, (normal, or gaussian distribution) and
    are completely normal.)

    You have shown a "frozen" box camera, and the picture would
    be true -- if the living eye were proven to be a "box camera".

    But no proof exists that the living, or natural eye is like that -- at
    all.

    Thus if the eye has a refractive state of EXACTLY ZERO (very rare),
    then a "plus 2" would in fact blur the eye-chart to about 20/140.
    True enough.

    For the "near" enviroment, the +2, for objects at 20 inches, would
    in effect be moved to optical "infinity".

    In fact, if you read NEI advocacy you will find that they realize
    that a "near" environment is a "problem" for the living, natural
    eye. So they make the statement that you should
    "look up" for 6 minutes out of every 60 minutes. (10 percent of
    the time looking at "infinity".)

    When I suggest that a 2 dipoter plus be used for all this
    "close work", it is simply to say that you should be
    "looking up" for 60 of the 60 minutes.

    And then the majority-opinion OD EXPLODE.

    That is clearly not "medicine" nor is this plus lens
    a "prescription".

    It is simply scientific common sense.

    Why do these majority opinion ODs have a problem with that?

    In fact, this becomes more a matter of personal choice or
    "judgment" that a "medical" issue. Why make it into
    a "medical" issue?

    Best,

    Otis
     
    otisbrown, Feb 3, 2006
    #18
  19. Christopher Zoettl

    acemanvx Guest

    Hey Christopher Zoettl, did you see my long reply below your post? I
    said everything I had to. I disagreed on alot of what you said!
     
    acemanvx, Feb 3, 2006
    #19
  20. Christopher Zoettl

    Quick Guest

    legal disclaimer? just in case it's quackery?
    Scientific common sense? I didn't know that science
    involved common sense. I thought common sense was
    what you used to make decisions in the absence of
    objective facts or insufficient information.
    Probably because it's not based on science and you have
    no common sense?
    Bzzzt, no legal out here. You're now saying that you're only
    suggesting a personal choice and not addressing a medical
    issue? Sounds like you're back peddaling.

    -Quick
     
    Quick, Feb 3, 2006
    #20
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