Understanding your vision. Everyone throws around the 20/20 or 20/ whatever number for their vision but few people outside us eyeball geeks really understand what 20/20 means so here is how it works.
This system of measuring vision was invented by Herman Snellen (eye surgeon) in 1862 and the eye chart is appropriately named after him, “Snellen Visual Acuity Chart” which I have had memorized for over 2 decades. In the Snellen system, everything is based on 20 feet or 6 meters. Past twenty feet your eyes are considered to be set for infinity so that is why we have 20 foot long exam rooms or mirrors set up in the exam room so that the total distance from the eye cart to the mirror on the wall to the patient is 20 feet. This is simply a space saving design.
To standardize vision testing, Dr. Snellen used an 8.75 mm (about 5/16 of an inch) tall letter at 20 feet and called that letter size 20/20 which is a comparison of what the patient sees to the standard acuity. In comparison, a patient who could only see the 17.46mm (8.73 X 2) from 20 feet would have 20/40 vision and twice that size 35mm for 20/80 vision. A patient with 20/200 could only see a 87.5 mm letter from 20 feet. To put it another way, a patient that is 20/400 must move to 20 feet from the chart to see the same size letter that a 20/20 person can see from 400ft.
You might still be feeling like what?? This can sound confusing but that is why Dr. Steve is here to help with figuring out your vision and giving you the best prescription to see at any distance! Call us to schedule your appointment with Dr. Steve.