What Is 20/20 Vision? What 20/40 and 20/200 Mean

20/20 vision means you can see clearly at 20 feet what should normally be seen at that distance: normal sharpness of vision on an eye chart. The top number is the testing distance, and the bottom number is the smallest letter size you can read. A person with 20/40 vision has to get within 20 feet to read a letter that should be clear at 40 feet. 20/20 isn't the same as perfect vision, though. It measures sharpness at one distance and leaves out side vision, depth perception, focusing, color vision and the health of the eye, which is why a comprehensive eye exam looks well past the chart.

Key takeaways

A 20/20 score means normal visual acuity, or sharpness, measured at 20 feet, the standard testing distance in the United States.
The bottom number is the smallest letter size you read, so 20/40 means getting within 20 feet to read a letter that should be clear at 40 feet.
Having 20/20 vision doesn't necessarily mean perfect vision, since the score leaves out side vision, depth perception, focusing, color vision and eye health.
If a school or DMV vision screening flagged your vision, book an eye exam to find out why.

What does 20/20 vision mean?

It means normal visual acuity, the clarity or sharpness of your vision, measured at a distance of 20 feet.

When you read letters on a distance chart, you're measuring visual acuity, and the result is written as a fraction. The top number is the testing distance. Doctors of optometry in the United States use 20 feet as the standard; in England, visual acuity is measured in meters and 6/6 is considered normal.

The bottom number is the smallest letter size you read. Each size is named for the distance at which a person with normal vision can read it, so 20/100 means you must be as close as 20 feet to see what a person with normal vision can see at 100 feet.

A smaller bottom number means sharper vision. With 20/15, you can read from 20 feet a line that a person with normal vision has to move to 15 feet to read. In our exams, each eye is also tested on its own.

What is 20/40 vision?

20/40 vision means you have to get within 20 feet to read a letter that should be seen clearly at 40 feet. Put simply, you need to be twice as close as someone with normal vision.

A common cause is a refractive error, a focusing problem such as nearsightedness, farsightedness or astigmatism. More than 150 million Americans have one, and in a study funded in part by the National Eye Institute, researchers estimated that 8.2 million Americans had vision problems in 2015 due to uncorrected refractive error.

So what 20/40 means depends on whether you had your glasses on. Measured without them, it may simply mean you need glasses or a stronger prescription; refractive errors like nearsightedness and farsightedness can be fixed with glasses, contacts or surgery.

Measured with the right glasses or contacts, 20/40 is different. Researchers count 20/40 or worse, even with full correction, as visual impairment, which affected 3.2 million Americans in 2015. The next step then is finding the cause, such as a cataract, which can make vision cloudy or blurry.

If a school or DMV vision screening flagged your vision, book an eye exam to find out why. In California, the DMV's vision screening standard is 20/40 with both eyes tested together, and 20/40 in one eye and at least 20/70 in the other.

20/200 means that for clear vision you would have to be 20 feet or closer to an object that a person with normal vision could see from 200 feet away. Legal blindness is 20/200 or worse in your better eye with glasses or contacts on, or a field of vision no wider than 20 degrees. Researchers estimated that 1 million Americans were legally blind in 2015.

A strong prescription that corrects to 20/20 isn't legal blindness, even if you can't read the top of the chart without your glasses. Our prescription explainer shows roughly how a diopter number translates to 20/xx.

When vision stays low even with the right lenses, it's called low vision: a vision problem that makes everyday activities hard and can't be fixed with glasses, contact lenses, or other standard treatments like medicine or surgery. Our low vision care uses magnifiers, lighting and contrast to help you get more from the vision you have.

Is 20/20 perfect vision?

No. Having 20/20 vision doesn't necessarily mean you have perfect vision. It describes how sharp your vision is at a specific test distance, and other vision skills contribute to how well you see:

Side (peripheral) vision
Eye coordination, how the two eyes work together
Depth perception
Focusing ability
Color vision

Near vision gets its own check. Some people see well at a distance but can't bring nearer objects into focus, because of farsightedness (hyperopia) or presbyopia, a loss of focusing ability. They can read 20/20 across the room and still struggle with a menu. Our guides to farsightedness and presbyopia explain both.

A sharp score can also hide distortion. With an irregular cornea, letters on the chart may be readable yet carry faint echoes, and lights can bloom with halos at night. Our page on higher-order aberrations explains why.

Can a child have 20/20 vision and still have a vision problem?

Yes. A child who sees clearly and has 20/20 vision can still have a problem with eye focusing, eye tracking or eye coordination; the vision skills needed for reading and learning go well beyond seeing the chart.

Screenings miss problems too. A vision screening can't diagnose an eye or vision problem; it can only show that a child may need a fuller evaluation, and screenings may miss as many as 60% of children with vision problems.

The AOA recommends a thorough eye exam between ages 3 and 5 and another when school starts, around age 5. After that, children should have an exam every year, because vision may change often during the school years.

Our pediatric eye exams measure how clearly each eye sees, in ways that work even before a child knows letters, and check focusing and eye alignment. If a child reads 20/20 but still struggles, vision therapy with Dr. Kevin Cohenmehr is one option we discuss.

How we check your vision at Cohenmehr Optometry

Reading the chart is only the start. In the refraction, the "which is better, one or two" part, our Los Angeles optometrists refine your distance, near and astigmatism correction with care, because a quarter-diopter can be the difference between glasses you tolerate and glasses you forget you're wearing.

Then we check how the two eyes work as a team and examine the eye itself: pressure, optic nerve, macula, retina, lids and tear film. None of that shows up on a chart. Retinal and corneal images taken in our office become your baseline for the next exam.

If your prescription changes, it goes straight to our optical down the hall. We recommend a comprehensive eye exam every year for most adults, and we'll tell you if you can stretch to every two.

Questions patients ask

Can you have 20/20 vision and be color blind?

Yes. Color vision is a separate skill from the sharpness that 20/20 measures. Color blindness, or color vision deficiency, means you see colors differently than most people. Most people who have it are born with it, and men have a much higher risk than women. Your eye doctor can usually tell with a simple test, and special glasses and contact lenses may help some people tell colors apart.

Can you have tunnel vision with 20/20 vision?

Yes. 20/20 measures sharpness at a test distance, and side vision is a separate skill. Glaucoma usually has no symptoms at first, and the vision it takes usually starts at the sides; a visual field test checks for that. Retinitis pigmentosa can narrow the field until only some central vision is left, called tunnel vision. If a dark shadow or curtain covers part of your vision, call us immediately for a same-day exam, or go to an emergency room when we're closed.

Will LASIK give me 20/20 vision?

Not always. The FDA notes that you may be under-treated or over-treated, and only a certain percent of patients achieve 20/20 vision without glasses or contacts. If you used reading glasses before surgery, you may still need them afterward, and some patients develop glare, halos or double vision that can seriously affect night vision. Through LASIK co-management we check your corneas and prescription before you meet the surgeon.

Why does my vision seem blurry when I can read 20/20?

20/20 is measured at one distance, so blur that comes and goes needs another explanation. Dry eye is one possibility: blurry vision is one of its symptoms, and it can happen if you spend a lot of time looking at a computer, tablet or phone. Long screen sessions can also cause blurred vision. Sudden loss of vision in one or both eyes, even if it comes back, sudden double vision, or any vision change with face drooping, arm weakness or trouble speaking can be a stroke: call 911. Other sudden blur that doesn't clear needs an emergency room; if it clears right away, call us for an exam.

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Written by

Dr. Bijan Cohenmehr, OD

Founder of Cohenmehr Optometry, in practice for over 40 years. He leads the practice’s dry eye care and myopia management. A graduate of SUNY College of Optometry.

About Dr. Bijan →

What Is 20/20 Vision? What the Numbers on an Eye Chart Mean