The results are used to determine if you need eyewear to correct your vision.
It’s part of a general assessment of your overall eye health.
This article explains how the eye chart works and what some benchmark results may mean.
Illustration by Joules Garcia for Verywell Health
Its name comes from Dr. Hermann Snellen, who invented the eye chart in 1862.
The number of letters on each row increases moving from top to bottom.
The size of the letters progressively decreases, allowing for more letters on each subsequent line.
Illustration by Joules Garcia for Verywell Health
The smallest row of letters that the patient reads accurately determines visual acuity in the uncovered eye.
The other eye also is tested, and both eyes are tested together.
It’s why normal human eyesight is sometimes expressed as20/20.
Your results are determined by the smallest line of letters you might accurately read on the chart.
What Is the 20/20 Line on an Eye Chart?
It seems like the answer should be straightforward, but the 20/20 line on an eye chart may vary.
Your vision results (acuity) will be expressed as a fraction.
To interpret your reading, it helps to think of the numbers in feet.
Modern optometricexam roomsare equipped with electronic eye reading charts, making it easier to produce accurate readings.
Vision requirements for driving vary by state.
Eye Chart Versions
Various types of eye charts are available besides the Snellen.
Some use pictures or patterns to measure visual acuity instead of letters.
Certain charts are used to measure distance vision and others measure near vision.
Other versions of this chart and alternate visual acuity charts are available.
Marsden J, Stevens S, Ebri A.How to measure distance visual acuity.Community Eye Health.
2014;27(85):16.
PMID: 24966459
American Academy of Ophthalmology.What Does 20/20 Vision Mean?
American Academy of Ophthalmology.All About the Eye Chart.
Aug 2019;2(82):1-6. doi:10.1038/s41746-019-0154-5
