StemCell Therapy

If you have glasses or contact lenses, your prescription is likely a baffling list of numbers and acronyms. Blame Ferdinand Monoyer.

The French ophthalmologist, born on this date (May 9) in 1836, was responsible for the diopter the unit of measurement we use to assess lenses and vision as well as modern-day eye charts seen in many opticians across the globe.

On what would have been his 181st birthday, Google has designed an animated Google Doodle to honour the anniversary. 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's signature is also hidden in the chart.

Although not the first to create an eye chart for ophthalmology Germany's Heinrich Kchler is widely accepted as the first to create a chart in 1836 using figures cut from calendars, books, and newspapers glued in rows of decreasing sizes Monoyer's legacy has been the one that has lasted the longest.

Subscribe to WIRED

Building on the work of Kchler, as well as the visual acuity chart design of Herman Snellen from 1862 used commonly in the US, Monoyer developed his chart to run alongside a visual acuity measurement known as the diopter. The diopter measures the distance you'd have to be from text to read it.

The Snellen Eye Chart was invented as a way to improve the subjective nature of vision testing and involved patients reading passages of text held their hands or held at a distance by the doctor. This test was dependent, however, upon the reading ability of the patient, typeface, and the fact the patient could guess the next word by reading a sentence. So he switched to letters.

Characters on the first Snellen Charts included: A, C, E, G, L, N, P, R, T, 5, V, Z, B, D, 4, F, H, K, O, S, 3, U, Y, A, C, E, G and L, and were Egyptian Paragons or slab serifs of contrasting line thickness with cross strokes on terminals.

Specsavers

Monoyer, who ran an ophthalmic clinic at the hospital in Nancy, France, took this initial idea and used it to introduce the first test-types corresponding to a decimal system in 1875. He selected his font style on a letter-by-letter basis because he didn't feel there was a need to select the same linear dimensions in every case. For example, a letter H that is as wide as it is high can look too drawn out, and he believed that if you're going to judge a person's vision by it, that letter needed to be as legible as possible.

In Monoyer's charts, every row represents a different diopter, from smallest to largest. A diopter indicates how powerful a lens is in order to properly focus light on a persons retina. It is officially defined as being the inverse of a persons 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.

Here is the original post:
Ferdinand Monoyer is the reason your eyesight is measured in decimals - Wired.co.uk

This entry was posted on May 14, 2017 at 2:46 am and is filed under Eye Sight & Vision. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed. |