Vision test chart
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- Snellen wall eye chart for 20 feet. Best for: Rooms with a 20 foot line of sight. See options on Amazon
- Snellen eye chart for 10 feet. Best for: Smaller rooms. See options on Amazon
- Pocket near vision card. Best for: Checking close-up reading vision. See options on Amazon
How a Snellen chart works
MedlinePlus describes the visual acuity test as finding the smallest letters you can read on a standardized Snellen chart from 20 feet away, with special charts used for shorter distances. You cover one eye at a time and read aloud the smallest line you can see, first without glasses or contacts and then, if needed, with them. Charts with numbers, lines or pictures are used for people who cannot read, especially children.
A near vision card, held about 14 inches from your face, checks close-up vision.
What the numbers mean
| Result | What it means | Next step |
|---|---|---|
| 20/20 | Considered normal visual acuity | Keep your regular eye exams |
| 20/40 | You read at 20 feet what normal vision reads at 40 feet | See an eye doctor about a possible prescription |
| Change from your usual line | Your vision may have shifted | Book an eye exam |
The top number is your distance from the chart, and the bottom number is the distance at which someone with normal eyesight could read the same line, per MedlinePlus. Missing one or two letters on a line still counts as reading that line. If your result is worse than expected, NEI says eye doctors can correct refractive errors with glasses, contact lenses or surgery after a comprehensive eye exam.
Setting up a chart at home
- Match the chart to the distance. Standard Snellen charts are read at 20 feet; if your room is shorter, use a chart made for the distance you have.
- Measure the distance from the chart to where you stand or sit, and mark the spot so each check is the same.
- Use the same setup each time so results are comparable from one check to the next.
- Test one eye at a time. Cover the other eye with your palm, a piece of paper or a small paddle, keeping both eyes open.
- Check with and without glasses if you wear them, and write down the line you reach for each eye.
Signs you need an eye exam
NEI says the most common symptom of a refractive error is blurry vision. Others include double vision, hazy vision, glare or halos around bright lights, squinting, headaches, eye strain, and trouble focusing when reading or looking at a computer. NEI notes some people do not notice symptoms, so regular eye exams matter, and that if you wear glasses or contacts and still have these symptoms you may need a new prescription.
NEI adds that presbyopia, trouble seeing up close, is common in adults ages 45 and older, and that most refractive errors such as nearsightedness usually start in childhood.
What a chart cannot check
A home chart only measures how clearly you see letters. NEI says many eye diseases have no symptoms or warning signs, and that a dilated eye exam is the only way to check for eye diseases early, when they are easier to treat. A full exam includes visual acuity plus a visual field test for side vision, an eye muscle test, a pupil response test, tonometry to measure eye pressure, and dilation to look inside the eye.
NEI recommends a dilated exam every 1 to 2 years if you are over age 60, are African American and over age 40, or have a family history of glaucoma. Most people with diabetes or high blood pressure need one at least once a year.
Wavy lines are a warning sign
NEI says that in late age-related macular degeneration (AMD), many people notice that straight lines start to look wavy or crooked, and may see a blurry area near the center of vision. NEI calls straight lines looking wavy a warning sign for late AMD and says to see your eye doctor right away if you notice it. People age 55 and older are more likely to have AMD, NEI says.
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What to look for when you buy
Snellen wall eye chart for 20 feet
Best for: Rooms with a 20 foot line of sight
Matches the standard 20 foot testing distance MedlinePlus describes.
Watch out: Measure and mark the distance before each check.
See options on AmazonSnellen eye chart for 10 feet
Best for: Smaller rooms
MedlinePlus notes special charts are used for distances shorter than 20 feet.
Watch out: Only use it at the distance printed on the chart.
See options on AmazonPocket near vision card
Best for: Checking close-up reading vision
Near vision is checked with a card held about 14 inches from your face.
Watch out: A card check does not replace a dilated eye exam.
See options on AmazonQuestions people ask
- What does 20/20 vision mean?
- You read at 20 feet what a person with normal eyesight reads at 20 feet; it is considered normal.
- How far should I stand from an eye chart?
- Standard Snellen charts are read at 20 feet; use a chart made for a shorter distance in smaller rooms.
- Are home vision tests accurate?
- MedlinePlus says home acuity tests have been found almost as accurate as an office test.
- Can an eye chart replace an eye exam?
- No. NEI says a dilated eye exam is the only way to check for many eye diseases early.
- What if straight lines look wavy?
- NEI calls this a warning sign for late AMD; see your eye doctor right away.
Sources
- Visual acuity test (medlineplus.gov), MedlinePlus Medical Encyclopedia
- Get a Dilated Eye Exam (nei.nih.gov), National Eye Institute
- Refractive Errors (nei.nih.gov), National Eye Institute
- Age-Related Macular Degeneration (AMD) (nei.nih.gov), National Eye Institute