|Summary: 20/20 vision is the standard eyesight measurement opticians use, thanks to Norman Snellen. Snellen’s procedure helps diagnose myopia or hyperopia using diopter values to accurately prescribe classes.|
My wife now has perfect vision after LASIK surgery. So, What is 20/20 vision? All your life you’ve woken up, opened your eyes, and checked your clock to find out how late you’ve overslept without ever giving it a second thought. Then one day you wake up and find the time on your clock isn’t as clear as it has been; Or maybe lately you’re finding it hard to see at night while you’re driving. Whatever the problem, like many things that occur with age, your once 20/20 vision is probably a thing of the past. But what is 20/20 vision anyway?
It was in 1862 that Norman Snellen first standardized eyesight and correction. Snell checked one’s visual acuity by having people stand 20 feet from a chart. He then recorded the smallest letter that most people with “perfect vision” could see. He labeled this size type “20,” hence 20/20 vision. Someone with 20/40 vision can only see at 20 feet what a person with 20/20 vision can see at 40 feet. If you’ve got “better than perfect” vision then your ratio would be 20/15 (or lower) – you can see at 20 feet what those with 20/20 vision would have to move closer for.
Although this technique can’t tell us everything about our vision, such as our ability to shift our focus suddenly between distance and what’s right in front of us, it is nonetheless where most opticians start when evaluating our sight
Using Snellen’s procedure, opticians are able to use diopter values, which measure the refractive power of the eye, to find the best lenses to correct your eyesight and bring you vision as close to 20/20 as possible. Ranging from -14 to +14, A higher positive number indicates myopia (near sightedness) and a negative indicates hyperopia (far sightedness). The greater the number, be it positive or negative, the worse eyesight one has. Thus when attempting to prescribe lenses for glasses or contacts usually a negative or positive number is part of that prescription.