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Medical Forum / General / Vision / May 2008Why don't ophthalmologists and optometrists use the Landolt C chart, instead of the Snellen chart?
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. > 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. 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. > > 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. [quoted text clipped - 4 lines] > would be more logical to test with actual letters that you read in > real life! But that's a guess I'm not sure. 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 <Protoman2050@gmail.com> wrote in news:59daca38-01bb-45ca-8341- 0131a3261528@h1g2000prh.googlegroups.com: > 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. 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.  SignatureScott Reverse name to reply > douglas <Protoman2...@gmail.com> wrote in news:59daca38-01bb-45ca-8341- > 0131a3261...@h1g2000prh.googlegroups.com: [quoted text clipped - 9 lines] > Scott > Reverse name to reply 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 <Protoman2050@gmail.com> wrote in news:d33d3a33-32f9-4386-90a8- 6bed5569050e@c19g2000prf.googlegroups.com: >> douglas <Protoman2...@gmail.com> wrote in news:59daca38-01bb-45ca-8341- >> 0131a3261...@h1g2000prh.googlegroups.com: [quoted text clipped - 13 lines] > the Landolt C or Bailey-Lovie chart? Will it give more accurate or > precise results? 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. SignatureScott Reverse name to reply > 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? Perhaps, but that degree of precision is only useful in certain circumstances and it requires a new set of rules, compared to "let me hear you guess at the letters on this line." Landolt C is pretty widely used and your doctor may be happy to test your acuity that way. There's a children's version called "broken wheel". -MT > > 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 [quoted text clipped - 10 lines] > > -MT What about Bailey-Lovie? Think he'd be happy about that? > > > 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 [quoted text clipped - 12 lines] > > What about Bailey-Lovie? Think he'd be happy about that? 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. > > > > 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 [quoted text clipped - 20 lines] > > - Show quoted text - That would be fun! "Test your acuity!!! $5 to test your acuity!!!!" > > > 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. > > 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? 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. Judy 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 in 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. Enjoy, > > > > 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. [quoted text clipped - 13 lines] > > Judy On May 5, 10:27 am, otisbr...@embarqmail.com wrote: > Subject: Accuracy of measurement. > [quoted text clipped - 41 lines] > > - Show quoted text - Making the image smaller somehow raises my acuity? That's a new one. YOUR RETINA IS NOT A COMPUTER SCREEN. Doug, 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 produced by you -11 diopter lens?? Enjoy, > On May 5, 10:27 am, otisbr...@embarqmail.com wrote: > [quoted text clipped - 48 lines] > > - Show quoted text - douglas schreef: > 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. 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) |
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