Normal Vision Test
Nearly everyone has had, or will have, a vision test at some point. From elementary school to the Department of Motor Vehicles to the medical examine to enter the armed forces our vision is assessed. The standard normal vision test used today, the Snellen Chart, was developed in 1862 by a Dutch ophthalmologist.
The Snellen Chart
The Snellen Chart is the standard in measuring visual acuity. The Snellen Chart is a row of block black letters on a chart that get progressively smaller by degree. The purpose of the test is to assess one's visual acuity by degrees. When taking the test, you hold your hand over one eye, so that each eye can be measured individually.
20/20 Vision
20/20 vision is what is considered standard vision up to age 70. The first 20 refers to the number of feet you are standing from the chart. The second number refers to what the normal person can see that many feet away. In other words, 20/20 is what an average person up to age 70 can read at 20 feet away. These letters are 3/8 inch in height and are in a specially created font where there is an equal amount of white around each letter block.
20/40 and Higher
If the second number is larger than 20, say 20/40, that means you see at 200 feet what the normal person can see at 40 feet. At this level you are still within the normal range and in most states can retain your driver's license without exception. You should be able to clearly see most printed materials. At 20/80 you can read most things 10 feet away. At 20/200 you are considered legally blind.
20/15 and Lower
If the second number is under 20, you have better than standard vision. However, its a misconception to think that 20/20 is the norm. 20/20 is the vision one is expected to retain until age 70, so really a younger person should have better than 20/20 vision. 20/15 vision would mean, you see at 20 feet what the average-sighted 70-year-old sees at 15 feet. Under 35, one should aim for 20/10 vision.
Other Vision Tests
The Snellen test does not take into account peripheral vision, depth perception, farsightedness (seeing clearly far but not close up) nor issues with focusing. Your optometrist has various ways including shining light in your eyes to see how your pupils react, using tools such as the ophthalmoscope to check the health of the back of your eye, assessing the movement of your eyes by following her finger, dilating your pupils, and exposing the eye to pressure. This is all done in an attempt to assure the eye is functioning at standard level, and if not, to provide the measurements necessary for glasses or contacts.
Tags: Snellen Chart, feet away, second number, better than, feet what, have better
