May 9, 2017
Ferdinand Monoyer’s 181st Birthday
Ferdinand Monoyer, born on this date in 1836, rose to prominence as one of France's most famous ophthalmologists. He developed the diopter, the unit of measurement for vision that's still used today. The diopter measures the distance you'd have to be from text to read it. Most notably, Monoyer devised an eye chart where every row represents a different diopter, from smallest to largest.
Monoyer was known to change the font of a particular letter if it didn't suit him; after all, if you're going to judge a person's vision by it, that letter had better be as legible as possible! If you look closely at today's Doodle, you might be able to spot a tribute to another of Monoyer's signatures: his name, hidden in the chart.