Google Doodle
Google's latest Doodle marks the 181st anniversary of the birth of renowned ophthalmologist Ferdinand Monoyer Google

If anyone has had to have their eyes tested, they owe a debt to the man being marked by Google in its latest Doodle.

Ferdinand Monoyer, the world renowned ophthalmologist developed the diopter, which is a unit that measures the distance you have to be from a text to read it.

He lent his name to the eye chart where every row represents a different diopter, as the text goes from smallest to largest.

If you look closely you can see Monoyer's signature hidden in the chart as Google marks the 181st anniversary of his birth.

The other most well known eye test is known as the Snellen chart, which was introduced around the same time.

According to Google's Doodle blog, if Monoyer did not like the font of a particular letter, he would change it, reasoning that to judge a person's vision, the letter needed to be a legible as possible.

Monoyer was from Lyon but studied at the University of Strasbourg before returning to his home city, where he died aged 76 in 1912 and is buried in the city's Cimetière de la Guillotière.