Eye health resource
What is 20/20 Vision and What Do These Numbers Mean?
20/20 describes a standard level of distance visual acuity, not perfect eye health or perfect vision. Learn what the numbers mean and what they do not measure.
Reviewed for accuracy by Justin Bazan, OD on .
20/20 vision describes a standard level of distance visual acuity. It does not mean your eyes are “perfect,” and it does not tell your eye doctor everything about your vision or eye health.
What Do the Numbers 20/20 Mean?
The first number is the testing distance: 20 feet in the traditional Snellen system. The second number represents the distance at which a person with standard visual acuity could read the same size letters.
If your acuity is 20/20, you can resolve at 20 feet the level of detail expected at 20 feet. If your acuity is 20/40, you need to be 20 feet away to resolve a line that a person with 20/20 acuity could resolve from 40 feet.
Is 20/20 the Best Possible Vision?
No. Some people can resolve smaller letters and measure 20/15 or even better. More importantly, visual acuity measures only one part of vision.
A person can read the 20/20 line and still have problems with peripheral vision, contrast sensitivity, color vision, depth perception, focusing, eye coordination, glare, or eye disease.
Can You Have 20/20 Vision and Still Have Eye Disease?
Yes. Glaucoma can reduce peripheral vision while central acuity remains excellent. Early diabetic retinopathy or retinal disease can also be present before the patient notices central blur.
That is why reading an eye chart is not a substitute for a comprehensive eye examination.
Does 20/20 Mean I Do Not Need Glasses?
Not necessarily. “20/20” may describe your vision with correction. Someone can have a significant glasses prescription and still achieve 20/20 acuity when wearing the correct lenses.
A person may also have 20/20 distance acuity and still need reading correction because of presbyopia.
What Is a Snellen Chart?
The familiar letter chart used for distance acuity is based on work by Dutch ophthalmologist Herman Snellen. The rows become progressively smaller, allowing the examiner to record the smallest level of detail the patient can reliably identify at the testing distance.
Modern offices may project or digitally display the optotypes rather than use a physical wall chart, but the visual-acuity concept is the same.
What Else Happens During an Eye Exam?
A comprehensive exam can also evaluate:
- your refractive prescription
- eye alignment and focusing
- eye pressure when appropriate
- the front structures of the eye
- the retina and optic nerve
- symptoms, medical history, and eye-disease risk
Park Slope Eye also offers Optos wide-angle retinal imaging, and OCT is available when cross-sectional imaging of the retina or optic nerve is useful.
What If My Vision Is Better or Worse Than 20/20?
A visual-acuity number is a measurement, not a diagnosis. If acuity is reduced, the reason might be an uncorrected prescription, cataract, retinal disease, corneal disease, amblyopia, or another condition. If acuity is excellent, that still does not prove that every part of the visual system is healthy.
If you want to know both how clearly you see and how healthy your eyes are, book an eye examination at Park Slope Eye.
Originally published . Substantially updated .