The only way to confirm you have 20/20 vision is to read a standardized eye chart from 20 feet away. If you can read the line marked “20/20” with each eye individually, your visual acuity meets the standard considered normal. You can get a rough idea at home with a printed chart, but a professional eye exam gives you a definitive answer.
What 20/20 Actually Means
The two numbers in a visual acuity score represent a ratio. The first number is always 20 because you’re standing 20 feet from the chart. The second number tells you how far away a person with normal vision would need to stand to read the same line you’re reading. So 20/20 means you see at 20 feet what a normally-sighted person sees at 20 feet. If your score is 20/40, you need to be at 20 feet to see what someone with normal vision can see from 40 feet away.
In countries using the metric system, the same measurement is called 6/6 vision, based on 6 meters instead of 20 feet. The concept is identical.
It’s worth knowing that 20/20 is not “perfect” vision. It’s the baseline for normal. Some people see 20/15 or even 20/10, meaning they can resolve details at 20 feet that most people would need to be closer to see. Research on the physical limits of the human eye suggests the sharpest possible vision is roughly twice as fine as 20/20, limited by the spacing of light-detecting cells in the center of your retina and the optics of the pupil itself.
Signs Your Vision May Not Be 20/20
Before you even test yourself, certain everyday experiences suggest your distance vision has slipped. Squinting to read road signs, difficulty recognizing faces across a room, or needing to move closer to a TV or monitor are all common clues. Headaches after extended periods of focusing, especially while driving or watching a screen, can also point to uncorrected refractive error.
One subtle sign people miss: closing or covering one eye to see more clearly. If you find yourself doing this without thinking about it, one eye is likely weaker than the other. Because the brain compensates by relying on the stronger eye, you can go years without realizing there’s a significant difference between them.
How to Screen Yourself at Home
You can do a basic screening with a printable Snellen chart, the familiar poster with rows of capital letters that get progressively smaller. The chart typically has 11 rows, starting with one large letter at the top and increasing in number and decreasing in size as you move down. Here’s how to set it up:
- Distance: Tape the chart to a wall at eye level and stand exactly 20 feet away. Measure the distance; guessing usually puts you too close.
- Lighting: The chart should be evenly lit with no glare or shadows across the letters.
- Cover one eye: Use your hand or a piece of cardboard to block one eye completely. Test each eye separately.
- Read downward: Start from the top and work your way to the smallest line where you can correctly identify all the letters. The line labeled “20/20” is your target.
- If you wear glasses or contacts for distance: Test both with and without your correction to see how each compares.
If you can read the 20/20 line with both eyes individually, your distance acuity is in the normal range. If you can’t get past 20/30 or 20/40, your vision would benefit from correction. Keep in mind that home screening is useful for catching obvious problems, but it’s not a substitute for a calibrated clinical test. Lighting, print quality, and distance accuracy all affect your results.
What a Professional Eye Exam Adds
An eye care provider doesn’t just check whether you can read small letters. The exam typically starts with the Snellen chart or a similar standardized chart, sometimes viewed through a mirror in smaller offices (the results are the same). But the real value of a professional exam is what comes next.
Your provider will use a device that flips between different lens options while you compare which makes the letters sharper. This process, called refraction, determines whether you need a prescription and precisely how strong it should be. Interestingly, the traditional letter chart can slightly overestimate your acuity by about 0.25 diopters. This is a small difference, but it means your “just barely 20/20” reading in a home test might actually fall slightly short under more precise measurement.
Beyond sharpness, a comprehensive exam evaluates things a letter chart can’t touch. Contrast sensitivity, your ability to distinguish objects from their background in low light or fog, depends on different visual pathways than the high-contrast black letters on a white chart. Peripheral vision, depth perception, color vision, and eye coordination are all separate from acuity. You can score 20/20 on the chart and still have trouble driving at dusk because your contrast sensitivity is poor, or miss objects approaching from the side because your peripheral field is narrowed.
20/20 Distance Vision Doesn’t Mean 20/20 Up Close
This catches many people off guard, especially after age 40. Presbyopia is the gradual stiffening of the lens inside the eye, making it harder to focus on nearby objects. It’s a universal part of aging, not a disease. The lens that once flexed easily to shift focus between a road sign and a phone screen becomes rigid enough that close-up tasks get blurry.
You can have flawless 20/20 distance vision and still need reading glasses. If you’ve noticed yourself holding menus at arm’s length, struggling to thread a needle, or needing brighter light to read fine print, presbyopia is the likely reason. It doesn’t mean your distance vision has changed. It means your focusing range has narrowed, and you now need separate correction for close work.
How Often to Get Your Eyes Checked
If you’re under 40, have no symptoms, and have no risk factors like diabetes or a family history of glaucoma, routine eye exams aren’t strictly necessary according to the American Academy of Ophthalmology. That said, a baseline comprehensive exam at age 40 is recommended for everyone. This gives your provider a reference point for detecting changes later.
After that baseline, the recommended schedule depends on age. Between 40 and 54, every two to four years is sufficient if nothing concerning turns up. From 55 to 64, the interval tightens to every one to three years. At 65 and older, every one to two years is recommended even if you feel your vision is fine. Many serious eye conditions, like glaucoma and macular degeneration, develop gradually and painlessly, so you won’t necessarily notice a problem until significant damage has occurred.
If you wear glasses or contacts already, you’ll naturally see your provider more often to keep your prescription current. But even people who have always had sharp vision should follow the age-based schedule, because acuity is only one piece of overall eye health.