Earlier this week on the 9th May an animated Google Doodle was created in honour of Ferdinand Monoyer’s 181st birthday. The doodle features a pair of eyes on the left, which form the 'O's in the word Google, alongside an eye chart on the right. As the eyes squint, the letters on the right become blurred. Monoyer is recognised for the development of the diopter; the unit of measurement for vision that is still used today!
Who was Ferdinand Monoyer?
Born in Lyon, France on the 9th May 1836, Monoyer rose to become one of France’s most famous ophthalmologists. During his impressive career, he served as an associate professor of medical physics at the University of Strasbourg from 1871.
Later, he was the director of the Ophthalmic Clinic of the Faculty of Medicine, the University of Nancy from 1872 to 1877. He was also Professor of medical physics at the Faculty of Medicine, the University of Lyon from 1877 to 1909.
What did he create?
A diopter is a unit of measurement for vision. The diopter measures the distance you’d have to be from text to read it. One of the most iconic forms of this is the decimal eye chart which features rows of letters that gradually go up in size.
Ferdinand Monoyer is also responsible for inventing one of the most commonly used eye charts back in 1872. Every row in the chart represents a different diopter, from smallest to largest. The pioneering ophthalmologist would ask patients to read up the chart until they could no longer distinguish characters.
The ophthalmologist also hid his own name inside the chart along either edge spelling out his first and last names, depicted in the Google Doodle. It appears when one reads vertically from bottom to top on each side.
The Monoyer chart has largely been replaced by the Snellen chart, which was invented soon after Monoyer's and flips the chart on its head by placing the largest letters at the top.
Why is diopter important?
A diopter indicates how powerful a lens is in order to properly focus light on a person’s retina. It is officially defined as being “the inverse of a person’s focal length in metres.”
“A shortsighted person with a –1.00 diopter lens can see objects at one metre clearly before they become blurred. Similarly, someone with a –2.00 diopter measurement needs a lens that's twice as powerful, meaning they can only see objects up to a 1/2 metre away clearly. A –3.00 lens would mean the person can only see a distance of up to 1/3 of a metre clearly, and so on. Most nearsighted people are in the range of -1.50 to -7.00 diopters.”
“Alternatively, longsighted people who need a +1.00 diopter lens can see objects at one metre clearly, but anything closer than that is blurred.”