Buying eyeglasses in the 1700s was tricky:
you had to diagnose the problem yourself and then pick the correct lenses. Some vendors helped customers along by scratching ages onto their spectacles, so that a 40-year-old would be steered to “40” lenses — the assumption being that everyone’s vision deteriorated at a similar rate as they grew older
But these shortcuts no longer sufficed in the mid-19th century, as doctors began to understand that patients needed bespoke lenses.
At a hospital in the Netherlands, Dr. Franciscus Donders devised a method for diagnosing vision problems: he would ask people to gaze at a chart on a distant wall and report what they could see. Apparently too busy to make the chart
himself, he enlisted the help of a colleague, Herman Snellen.
Snellen first printed up a chart with dingbats — squares, circles,
plus signs — of various sizes, but that proved to be a bad idea.
“When you look at a symbol, how do you describe it?” says
August Colenbrander, a scientist at the Smith-Kettlewell Eye
Research Institute who has researched the history of the eye
chart. (It was probably easy to cheat, too.) In the end, Snellen
realized that letters would work best.
The chart spread all across Europe, an instant hit. “The first big
order was from the British Army, in 1863 or so,” Colenbrander
says. “Obviously the soldiers who fired their muskets had to be
able to see.” Soon after that, printers everywhere copied it. A
low-tech solution to a complex problem, the chart has remained
popular because it was cheap and easy to use. But widespread
reproduction and success are two different things. The EFPTOZ
chart (pictured here) has practically become iconic, undermining
its medical value, Colenbrander says. A recognizable eye chart is
not a very useful one.
By PAGAN KENNEDY
May 24, 2013
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