Why don't ophthalmologists and optometrists use the Landolt C chart,instead of the Snellen chart?

Discussion in 'Optometry Archives' started by douglas, May 2, 2008.

  1. douglas

    douglas Guest

    Why don't ophthalmologists and optometrists use the Landolt C chart,
    instead of the Snellen chart? It's harder to cheat w/ the Landolt C.
    douglas, May 2, 2008
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  2. douglas

    Zetsu Guest

    It could be because in everyday routine average real life mundane
    tasks no one is going around reading Cs in various different
    directions, they're going to be reading actual letters! So, I guess it
    would be more logical to test with actual letters that you read in
    real life! But that's a guess I'm not sure.
    Zetsu, May 2, 2008
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  3. douglas

    douglas Guest

    Yes, but the point of that chart is to test your acuity. And,
    according to House, patients lie. This is very common w/ subjective
    refractions. And w/ governmental eye exams, like those for the DMV. If
    the DMV switched to the Landolt C chart, no one could cheat on the
    acuity section of the driver's license exam. The Landolt C is superior
    to the Snellen in that respect. Also, in the Snellen the number of
    letters increases while the size decreases introduces two variables,
    rather than just one, which should be letter size.

    "In 1888 Landolt proposed the Landolt C, a symbol that has only one
    element of detail and varies only in its orientation. The broken ring
    symbol is made with a "C" like figure in a 5 x 5 grid that, in the
    20/20 optotype, subtends 5 minutes of arc and has an opening (oriented
    in the top, bottom, right or left) measuring 1 minute of arc. This
    proposal was based in the fact that not all of Snellen's optotypes
    were equally recognizable. This chart is actually the preferred visual
    acuity measurement symbol for laboratory experiments." So there.
    douglas, May 2, 2008

  4. They can get what they need from the Snellen, and its easy to use.

    For all serious (i.e., scientific) assessments, though, a Vernier acuity
    task like the Landolt C really is the way to go.
    Scott Seidman, May 2, 2008
  5. douglas

    douglas Guest

    Still, what if I ask my optometrist and ophthalmologist to test me w/
    the Landolt C or Bailey-Lovie chart? Will it give more accurate or
    precise results?
    douglas, May 2, 2008
  6. You don't need more accuracy to get the right correction. Vernier acuity
    tests allow for better comparisions between studies and rule out any
    cognitive influences on the tests.
    Scott Seidman, May 2, 2008
  7. douglas

    Jan Guest

    douglas schreef:
    The first part is a wrong assumption.
    It's a nice test when having a analfabetic in the chair.
    Also handy when the examiner and the client don't speak the same
    language or speaking is a problem.

    For the second part, it's only more difficult to guess, cheating is not
    the issue.

    Jan (normally Dutch spoken)
    Jan, May 2, 2008
  8. douglas

    douglas Guest

    What about Bailey-Lovie? Think he'd be happy about that?
    douglas, May 3, 2008
  9. douglas

    Zetsu Guest

    Well, it's his job after all to examine and test people's vision. So
    being specialized in that field, I don't see him having any difficulty
    testing you with different acuity charts if you requested it. But
    also, you could print your own charts and test yourself! Because it's
    more fun that way! Or get a family member to test you or whatever.
    Zetsu, May 3, 2008
  10. douglas

    douglas Guest

    That would be fun! "Test your acuity!!! $5 to test your acuity!!!!"
    douglas, May 3, 2008
  11. douglas

    Dr Judy Guest

    More accurate what? Accuracy of determination of refractive error is
    not a function of the chart used. Best corrected acuity measurement
    might be slightly more precise, but is of little practical benefit.

    Some optometrists or ophthalmologists mihgt have a Landolt C, few will
    have a Bailey Lovie chart, so even if you ask, they are unlikely to be
    able to do it. Researchers and low vision specialists are more likely
    to have a Bailey Lovie chart.

    Dr Judy, May 4, 2008
  12. douglas

    otisbrown Guest

    Subject: Accuracy of measurement.

    1. Visual Acuity: read Snellen where 3/8 inch letters are 20/20, and
    3/4 inch letters are 20/40.

    2. Refractive STATE: For that you will need plus and minus lenses
    1/4 diopter increments. From 20/60 (let us say) you determine the
    minimum minus required to just-clear the 3/8 inch line.

    Judy> More accurate what? Accuracy of determination of refractive
    error is
    not a function of the chart used.

    Otis> You are correct. It is determined by the person using his
    own "test" lenses to make an accurate measurement of his
    refractive STATE.

    Judy> Best corrected acuity measurement
    might be slightly more precise, but is of little practical benefit.

    Otis> Best-Corrected value (can produce 20/10 vision) might mean
    -1 to -1.5 diopters more minus.

    otisbrown, May 5, 2008
  13. douglas

    douglas Guest

    Making the image smaller somehow raises my acuity? That's a new one.
    douglas, May 6, 2008
  14. douglas

    otisbrown Guest


    You are wearing a -11 diopter lens. Does that make the image
    on your retina "smaller"??

    And is that image seem sharper to you from your "smaller" image
    by you -11 diopter lens??

    otisbrown, May 8, 2008
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