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Medical Forum / General / Vision / March 2005Snellen vs Sloan?
What's the difference between Snellen and Sloan eyecharts? Why are there two?  SignatureRon Hardin rhhardin@mindspring.com On the internet, nobody knows you're a jerk. > What's the difference between Snellen and Sloan eyecharts? Why are > there two? There are more than just two visual acuity measuring charts, but Sloan and Snellen style are the most common. New charts are designed to correct errors in previous charts. The Sloan style charts modify the older Snellen style by correcting some of the problems with Snellen style. Sloan style use non serif letters, more letters per line, control the white space around the letters and, since some letters are easier to recognize than others, controls for difficulty of letter recognition per line. Dr Judy > The Sloan style charts modify the older Snellen style by correcting some of > the problems with Snellen style. Sloan style use non serif letters, more [quoted text clipped - 3 lines] > > Dr Judy I've never heard of a Sloan chart - from your description, it sounds a lot like a Bailey-Lovie chart (5 letters per line) - is that the same thing? Dom >> The Sloan style charts modify the older Snellen style by correcting some >> of the problems with Snellen style. Sloan style use non serif letters, [quoted text clipped - 6 lines] > I've never heard of a Sloan chart - from your description, it sounds a lot > like a Bailey-Lovie chart (5 letters per line) - is that the same thing? Not a scientific as the Bailey-Lovie but it does have 5 letters per line for more lines than the Snellen. I think Bailey & Lovie started with the Sloan chart and added further modifications. It is also sized for a 10 foot test distance if you don't have a mirror set up. I keep a plastic Sloan Chart in the office to use when people just miss the BCVA requirement for driving when reading the projected chart. Often they will read one or two lines better with the paper chart. http://www.precision-vision.com/Products_List.asp?ProductCategory=SLOAN%20Charts Dr Judy > I keep a plastic Sloan Chart in the office to use when people just miss > the BCVA requirement for driving when reading the projected chart. Often > they will read one or two lines better with the paper chart. > Dr Judy Dr Judy, maybe your plastic chart is of a higher contrast. Often the screen on which the characters are projected is placed in a wrong angle to the projector. The screen is to be mounted in the same angle to the mirror as the projector ( angle in is angle out) When you only use a screen and a projector, be sure you have the screen mounted perpendicular to the light beam. You be surprised how often this makes the difference in contrast and so influence the acuity numbers. SignatureJan (normally Dutch spoken) >> I keep a plastic Sloan Chart in the office to use when people just miss >> the BCVA requirement for driving when reading the projected chart. Often >> they will read one or two lines better with the paper chart. >> Dr Judy > > Dr Judy, maybe your plastic chart is of a higher contrast. Yes, any paper or plastic chart will be better contrast that a projected chart, even with all the angles correct. That's why I like to have the plastic chart available. Dr Judy > Often the screen on which the characters are projected is placed in a > wrong angle to the projector. [quoted text clipped - 4 lines] > You be surprised how often this makes the difference in contrast and so > influence the acuity numbers. > There are more than just two visual acuity measuring charts, but Sloan and > Snellen style are the most common. New charts are designed to correct > errors in previous charts. Yes, in fact, the practicer of perfect sight without glasses are advised to use many different charts in order to find out which chart IS READ BEST. In this way, when you look at it, you RELAX your mind, and the eye focusses better. > The Sloan style charts modify the older Snellen style by correcting some of > the problems with Snellen style. Sloan style use non serif letters, more > letters per line, control the white space around the letters and, since some > letters are easier to recognize than others, controls for difficulty of > letter recognition per line. Serif letters are MUCH BETTER than non serif. Discard the charts which have no serit. The fact that some letters are more easy to recognize does not mean that a chart should have only "difficult" letters. There must be variety because what is EASY for ONE PATIENT may be DIFFICULT for ANOTHER. http://TheCentralFixation.com |
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