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The Snellen Eye Chart

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Do you know what a Snellen Eye Chart is? Most of us just refer to it as "the chart" at the eye doctor's office. That white piece of paper with all the letters on it that measures your visual acuity is the Snellen Eye Chart. The chart is named after Hermann Snellen, a Dutch ophthalmologist who developed this chart back in 1862. Acuity charts are still used for different types of vision exams today. Read on for some more background on the Snellen Eye Chart and its humble beginnings. 

- History and Background of the Snellen Eye Chart

Vision testing used to be not as accurate as it is today. Patients were basically expected to self diagnose and pick out their own eyeglasses. Vision was thought to deteriorate at the same rate for everyone, so if you were 40, you would generally pick out eyeglasses that had "40" etched on the side.


At a hospital, Dr. Franciscus Donders saw a need to change at a time where the field of vision was ripe for improvement. He came up with a way to diagnose vision: asking people to look at a chart and say what they saw there. At the time that he invented the eye chart, ophthamalmology was on the birnk of its golden age of organ based specialty. He was too occupied to make the chart himself, so he enlisted Herman Snellen.


Snellen developed the Snellen Chart in order to measure visual performance against a standard of reference that could be repeated. The Snellen Eye Chart filled a much needed gap and in 1862 and prior, there were only reading tests for sight and no objective standards. Snellen first made a chart that consisted of dingbats, various symbols of various sizes. He later changed the dingbats to letters, as they were able to be universally described. Snellen designed letters placed on a five by five grid, calling them optotypes, and created the reference standard of 20/20. The chart was rectangular and lined with seven rows of letters that grew smaller as one moved down the chart.


The chart instantly was a success, with orders arriving from everywhere, including the British Army in 1863 to detect whether their soldiers would be able to see and thus fire their muskets effectively. Printers all over were soon producing the chart. It was a simple solution and it was not difficult to print these charts, since they were both technologically easy to make and cheap to produce. A version of the Snellen Eye Chart has been used ever since.



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