Difference Between Snellen and Sloan Eye Chart

Sep 27, 2021 | Optometry

Difference Between Snellen and Sloan Eye Chart

Eye doctors everywhere are familiar with the eye chart. Whether you’re an ophthalmologist or optometrist, you’ve likely had to perform an eye test with an eye chart at some point. But did you know that there are multiple types of eye charts? There are many types, but the main two to focus on are the Snellen eye chart and the Sloan eye chart. Here are some of the differences between Snellen and Sloan eyes charts.

Snellen Eye Chart

You’ll recognize the Snellen chart when you see it, whether you use it in your own practice or if you’ve ever been on the receiving end of an eye exam. The Snellen chart is the most popular type of eye chart and is the one that most people picture when an eye test comes to mind. An eye doctor uses this chart to measure visual acuity by recording the amount of detail that the patient can describe. The chart consists of 11 lines of letters, which are also known as “optotypes” in the optometry field. The Snellen chart test requires the patient to cover one eye and read the letters row by row until they can’t make them out.

Sloan Eye Chart

The Sloan eye chart is another tool eye doctors use to test visual acuity. This chart uses optotypes as well, though these letters are roughly the same sizes. Sloan letters form a modern-looking chart, which many school nurses use to test students’ eyesight. This chart is becoming used increasingly for modern eye exams. If you are familiar with the Landolt C Rings exam, the optotypes for this chart are based on the C Rings optotypes.

Eye Chart Differences

The major differences between the Snellen and Sloan eye charts lie in the optotypes themselves. Snellen optotypes use bold, larger lettering with serifs—the smaller strokes attached to the ends of a letter symbol. Sloan optotypes don’t utilize serifs; rather, they use a more modern design and font. This, combined with their origins from the C Rings exam, may make them more accurate than the Snellen chart, some studies say.

Does this clear up the difference between Snellen and Sloan eye charts? These are two of the most common eye charts you will find in the ophthalmology practice, so they are good to be familiar with. These are just the beginning of ophthalmic materials—check out Automated Ophthalmics Inc. for a more thorough look into more types of ophthalmic supplies.