Lens Distance Vision Limits?

Discussion in 'Eye-Care' started by Gene Goldenfeld, Nov 10, 2003.

  1. I recall during two recent eye exams by different optometrists that each
    said there's a limit to how much correction can be made with a lens, in my
    case progressive. My recollection is they said something like 20-15. The
    full meaning of what they were saying excaped me at the time, seeming a bit
    abstract while sitting in a chair looking at letters. Before getting
    progressives three years ago, distance was a particular strength. Now that
    I have a new pair of Comforts that work well overall, I notice a little
    blurriness at a distance, by which I mean, say, 200 yards on out, that
    distance where one wants to read an upcoming freeway sign to prepare in
    time. Looking higher up in the lens doesn't have any effect. Is this what
    the ODs were talking about, that only so much can be done for distance
    vision?

    The prescription is

    plano -.75 95
    -.25 -1.00 86
    +2.00

    Thanks,
    Gene Goldenfeld
     
    Gene Goldenfeld, Nov 10, 2003
    #1
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  2. Gene Goldenfeld

    Otis Brown Guest

    Dear Gene,

    20/15 is very good vision, and exceeds the standard
    set about 130 years ago. The 20/20 standard was established
    by what the average person could be corrected-to.

    This is character that subtends 5 minutes of arc at 20 feet
    or 6 meters.

    Or, by calculation, 3/8 inch characters at 20 feet.

    The military (during WWI) set a minimum standard of
    10 minutes-of-arc, or 20/40 vision.

    You substantially exceed these limits -- you have
    very good distant vision indeed.

    There are a few fighter pilots and baseball players who
    can see 20/10 -- but that is exceptional.

    If you wish to check this, you should use your own
    eye chart. You would be certain to verify the
    high quality of your distant vision in daylight.

    Best,

    Otis
    Engineer

    *****
     
    Otis Brown, Nov 11, 2003
    #2
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  3. It's late at night, I'm tiring and tempted, well... Otis, I don't think
    you've shed any light on the question I asked or the problem I've noticed.

    I'm hoping for a better understanding of what the optometrists said and if
    it's relevant to what I'm experiencing.

    Gene
     
    Gene Goldenfeld, Nov 11, 2003
    #3
  4. Gene Goldenfeld

    Otis Brown Guest

    Dear Gene,

    Perhaps the problem is the "progressive".

    Why not request a "single vision" lens from
    your OD and see if that works better
    than the progressive.

    Best,

    Otis
    Engineer

    *****
     
    Otis Brown, Nov 11, 2003
    #4
  5. Gene Goldenfeld

    Dr Judy Guest

    What they meant was that an individual eye has a best corrected acuity that
    is limited by eye factors like internal aberration, photoreceptor spacing,
    pupil size, lens clarity etc and that glasses do not exist that will make
    that best corrected better.

    Your ability to see a freeway sign in time to react is limited by the size
    of the letters on the sign, your distance from the sign, speed of travel,
    which lane your are in (ie how many lanes you need to change in reaction),
    your reaction time and then things like cleanness of your car windshield,
    light conditions, angle of the sun, volume of other traffic, how close cars
    are spaced etc, etc. You actual best corrected visual acuity takes a back
    seat to those other factors. Remember, at 60 mph, you are travelling at a
    mile a minute or 30 yards/sec. If you start to read a sign 200 yards away,
    you have about 6 seconds to read it, make a decision and take action before
    you pass it; your motor reactions will take up 2-3 seconds after you make
    your decision and the car will have its own response time.

    In general, I find that if you are travelling quickly in the left lane on a
    unfamiliar route and are relying on freeway signs to decide when to turn
    off, you will have trouble seeing a sign soon enough to move right for your
    exit. It pays to study the map ahead of time to know which two exits are
    preceeding yours and move right well in advance.

    Dr Judy
     
    Dr Judy, Nov 11, 2003
    #5
  6. Thanks. What concerns me is that this inability to see a normal overhead
    freeway sign clearly enough even to guess its contents at a reasonable
    distance seems both a change with these new glasses and scary (as in
    dangerous). That 200 yards was an estimated minimum , based on driving.
    Two hundred yards is sometimes way too little to react appropriately in
    multilane freeway traffic, and I'm not a reckless or especially fast
    driver. Moreover, while standing still outside, I notice that even at 100
    yards a large neon sign shows a little extra outline. I'm sorry, but life
    is not so predictable to be able to have it all mapped out on paper or
    mentally ahead of time. I've had these new progressives 5 days now and
    otherwise find them great.

    Gene
     
    Gene Goldenfeld, Nov 11, 2003
    #6
  7. Gene Goldenfeld

    Dr Judy Guest

    major snip
    If this is a change from the previous pair, and the outline is not visible
    with previous pair, take them back to fitter for adjustment. The frame may
    need minor tilting to position it properly in front of your eyes. If the
    effects existed with previous, it may be the normal distortions found in
    progressive or something in your eye like early lens changes.

    Dr Judy
     
    Dr Judy, Nov 12, 2003
    #7
  8. The frames have already been tilted 15 degrees. I'm planning to stop by
    the optometrist to check there first. I'd like to find out what's going
    on, whatever that may be. Thanks,

    Gene
     
    Gene Goldenfeld, Nov 12, 2003
    #8
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