Acuity readings plus/minus a few letters.

Discussion in 'Optometry Archives' started by Don W, Oct 11, 2006.

  1. Don W

    Don W Guest

    If one is having an Snellen test, and the reading comes out 20/100 minus
    1, that means one letter has been lost in reading the 20/100 line. Truth?
    And how is that reading should be converted to 20/? . Where ? is a
    singular number. If so, how do we interpolate to the actual reading??

    Now, if the reading is 20/100 plus one. Just exactly what does that mean?
    Does that mean one is reading the 20/100 line totally and one more letter of
    the next line? And does "plus" have any reasonable meaning since the letter
    height of the next line might vary?

    Don W.
     
    Don W, Oct 11, 2006
    #1
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  2. Approximately true. It can also indicate 20/100 but possibly with some
    guesswork involved, or a very blurred 20/100.
    There is no rigid standard in acuity since it it such a subjective and
    necessarily variable measurement.
    You could convert 20/100- to 20/150 and nobody would get too excited,
    since most snellen charts have 20/100 letters but many jump from there
    20/200.
    Yes. Usually, it means just one letter was seen on the next line. If
    they read 2 letters on the 20/80 line, it would normally be written
    20/20 ++ or 20/20 +2
    See above. All Snellen acuity has reasonable but not necessarily
    precise meaning.
     
    William Stacy, Oct 11, 2006
    #2
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  3. Don W

    Ace Guest


    Your a little better or worse than 20/100. Perhaps 20/80 if better,
    perhaps 20/120 or 20/150 if worse. There needs to be at least the
    20/150 line between 20/100 and 20/200, but many eyecharts dont! :(
     
    Ace, Oct 11, 2006
    #3
  4. Don W

    Don W Guest

    So would people get excited if vision went from 20/100 to 20/200?

    In a lot of the clinical trials they are talking about the gain or loss of
    so many _letters_ , not lines (e.g., Lucentis). Is that not cutting it
    rather thin for "subjective"?

    Don W.
     
    Don W, Oct 12, 2006
    #4
  5. Don W

    serebel Guest


    Don, you're answering a retard who has no clue as to what he's talking
    about.
     
    serebel, Oct 12, 2006
    #5
  6. Don W

    otisbrown Guest

    Otis> Or, just cut the distance in 1/2. Thus the 20/50 (size) becomes
    20/100, 20/60 (size) is 20/120, etc.

    Otis
     
    otisbrown, Oct 12, 2006
    #6
  7. Don W

    Ace Guest


    That wont work, the chart has to be read at optical infinity. At 10
    feet there is 1/3 diopter accomodation. I can see more than twice as
    well from 10 feet vs. 20 feet because the 1/3 diopter accomodation
    "cancels" out -.33 diopters of myopia.
     
    Ace, Oct 12, 2006
    #7
  8. Don W

    Don W Guest

    Thanks to Dr. Judy (and others) for clearing up this confusion. I think
    in going to the plus side, specifying the number of letters on that next
    line (and the size) nails it down completely.

    There is one other area in acuity reporting that is bothersome. I am
    reading the results of the Lucentis trials. And therein is claimed a gain
    of so many letters after so much usage. But they never specify in going
    from what line to what other line to get the gain 6 letters. The gain of 6
    letters is, of course, an average. (and maybe Snellen or not). But this
    seems to be an extremely confusing way to state improvement, statistically.

    Don W.
     
    Don W, Oct 13, 2006
    #8
  9. Don W

    Don W Guest

    OK, agreed as to the variability of results.

    Let me see if I can clear up how I am confused. When they publish the
    curves for the advantages of Lucentis, they are published as to the gain of
    the number of letters as a function of time (monthly). These gains (I
    presume), can be from 20/200, or from 20/100 or whatever. So gains are
    really some kind of differential from some line in the Snellen chart (if
    they used that) to some other line. And then these gains are then averaged
    to show the average gain for that month. It seems they are averaging apples
    and oranges. If someone is at 20/200 and gains 6 letters in the Snellen
    chart, that is much more dramatic than someone who is 20/50 and then gains
    6. At least this is what it seems like.

    Don W.
     
    Don W, Oct 14, 2006
    #9
  10. Don W wrote:
    If someone is at 20/200 and gains 6 letters in the Snellen
    Your example isn't clear. That is, snellen charts go from 20/200 to
    20/100 or 20/150, and typically the 20/100 or 20/150 size letters have
    only 4 letters or so on the chart. "gains 6 letters", without
    specifying WHICH size letters is kind of meaningless, unless one has a
    random letter generating chart and you really mean something like "gains
    6/12 of 20/100" or 6 out of 12 presentations of that size.

    Certainly 20/200 to 20/100 sounds more dramatic than 20/50 to 20/40, but
    in the real world of seeing, the latter may be more significant than the
    former.

    w.stacy, o.d.
     
    William Stacy, Oct 14, 2006
    #10
  11. Don W

    Don W Guest

    Don W, Oct 14, 2006
    #11
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