Google on Tuesday paid tribute to Ferdinand Monoyer, a French ophthalmologist who showed us the way to measure eye sight.
Born in 1836, Monoyer developed the diopter, the unit of measurement for vision that is still used today.
The diopter measures the distance you would 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.
"Ferdinand Monoyer, born on this date in 1836, rose to prominence as one of France's most famous ophthalmologists," Google said.
"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," Google added.
According to the American Academy of Ophthalmology, the most commonly used eye chart, however, is the Snellen chart which Dutch eye doctor Hermann Snellen developed in the 1860s