The Meaning of 20/20
The term 20/20 vision comes from the Snellen eye chart, developed by Dutch ophthalmologist Herman Snellen in 1862. The fraction describes visual acuity — the sharpness or clarity of your vision.
The first number (20) is the distance in feet at which you are standing from the chart. The second number is the distance at which a person with normal vision can read the same line. So 20/20 means you can read at 20 feet what a person with normal vision reads at 20 feet.
Is 20/20 Perfect Vision?
Not necessarily. 20/20 is considered normal, not perfect. Some people have 20/15 or even 20/10 vision — meaning they can see at 20 feet what most people need to be 15 or 10 feet away to see. Visual acuity is just one aspect of vision; color perception, depth perception, and peripheral vision are equally important.
What Do Other Scores Mean?
- 20/20 — Normal vision
- 20/40 — You need to be at 20 feet to see what a normal person sees at 40 feet. Many states require at least 20/40 to drive without corrective lenses.
- 20/100 — Significant impairment; glasses or contacts are strongly recommended.
- 20/200 — Legal blindness threshold in the United States (with best correction).
How Is Visual Acuity Tested?
In a clinical setting, an optometrist uses a Snellen chart — a poster with rows of letters that get progressively smaller. You cover one eye and read the smallest line you can see clearly. The result is your visual acuity score for that eye.
Online tools like VisionCheck use a digital Snellen-style chart to give you a preliminary acuity estimate from home. While not a substitute for a clinical exam, it can indicate whether a professional evaluation is warranted.
Can Vision Change Over Time?
Yes. Vision commonly changes during childhood and adolescence as the eye grows, and again after age 40 when the lens loses flexibility (presbyopia). Regular eye exams — at least every two years for adults — are the best way to track changes.
Sabroe Enterprise
VisionCheck Eye Health Team