# The hidden math behind your DMV’s eye test

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## That familiar eyesight chart revolutionized vision testing, and we went to ridiculous lengths to test it out

At least once in your life, you must have squinted at the eye chart at the doctor’s office or DMV, trying to make out the blurry bottom line. The test seems simple enough, right? Read a random string of consonants and vowels on one line, then repeat the process with the line below until you can’t make out the letters anymore.

Turns out, there’s some very precise math that determines the size and arrangement of those block letters in order to test your ability to see details — known as your “visual acuity.” First developed in 1862 by Dutch ophthalmologist Herman Snellen, the prototypes of this eye chart began with abstract shapes. Eventually, the chart included those familiar block letters.

One of Snellen’s big accomplishments was standardizing the eye chart so that others could use the same principles to develop their own tests. So we decided to give it a try. In the video above, we trace the eye chart back to its origins and take a close look at the biology of visual acuity and the math that goes into testing its limits. Then, we go to ridiculous lengths to test my own eyesight. Spoiler alert: it’s awesome.