How to Do an Eye Test at Home: How Far Away Should Your Phone Be? 7 Tips for Accurate Results
"Distant writing has been looking blurry lately." "My licence renewal is coming up; will I pass?" Often you want to check for yourself before going to an eye doctor. Even on a phone or computer screen, if you match the size of the Landolt ring (the letter C) to the distance correctly, you can estimate your visual acuity on the same principle as a clinic's eye chart. This article covers how to do an eye test at home, how far to stand from a phone, a computer or a printed chart, why results drift and 7 tips for accurate measurement, how to read your numbers, and signs that you should see an eye doctor.
What a home eye test can and can't tell you
In eye clinic and school tests, you look at C-shaped Landolt rings from a set distance, and your acuity is the smallest ring whose gap direction you can make out. All that matters is the relationship between ring size and distance, so paper or screen makes no difference as long as size and distance are right. The point of testing at home isn't to replace an eye doctor but to check easily whether your eyesight has dropped since last time, or whether it's likely to meet driving licence or school standards.
| What you can find out at home | What you can't find out at home |
|---|---|
| Approximate acuity for the right eye, left eye and both eyes (0.1–2.0) | The strength of short-sightedness, long-sightedness or astigmatism (in dioptres) |
| Whether you see worse than last time | Whether you have cataracts, glaucoma, retinal disease, etc. |
| Whether your vision with glasses or contacts (corrected acuity) is good enough | The exact values needed to prescribe glasses or contacts |
| Whether there's a big difference between your eyes | Depth perception, visual field and colour vision |
| Whether you might have astigmatism (radial chart), and whether close-up vision is getting harder | Eye pressure and the condition at the back of the eye |
How far from a phone, a computer or a printed chart?
Eye clinic and school tests in Japan are normally done at 5 m. But few homes have a 5 m space, and a phone screen can't fit the large rings needed at 5 m (over 7 cm across for 0.1). If you shorten the distance, drawing the rings smaller in proportion gives the same test. The gap in the 1.0 ring is 1.45 mm at 5 m, 0.58 mm at 2 m and 0.29 mm at 1 m.
| Device | Recommended distance | Why |
|---|---|---|
| Phone | 1–2 m | You can stand it on a desk or stand an arm's length or so away, and even the large 0.1 ring fits on screen |
| Tablet | 1.5–3 m | The bigger screen lets you sit further away. Answer with a separate device or keyboard in your hand |
| Computer | 2–3 m | Many screens have coarse pixels, so up close they may not be able to draw steps finer than 1.0 |
| Printed chart | 3 m or 2.5 m (to suit the room) | Paper has no pixel limit, so you can measure fine steps even in a room without 5 m of space |
| Close-up vision (near acuity) | 30 cm | A guide to presbyopia: check whether you can read fine print at about the distance you hold a phone |
In the Visual Acuity Test (Landolt Ring) tool, choosing a distance shows the range you can measure, such as "this screen can measure 0.1 to 2.0". A recent phone with fine pixels can draw up to 2.0 even at 1 m, for example, but a computer monitor may only manage about 0.8 at 1 m. The basic rule: move further away to measure finer steps, and move closer if the large steps don't fit on the screen. The ring-size calculation for each distance is explained in detail in Landolt ring size and distance: making a 3 m or 2.5 m eye chart.
Steps for an eye test at home
- 1
Calibrate the screen's real size
"1 mm on screen" differs between phones and computers. Hold a credit card or transit IC card (85.6 mm wide) or a 1-yen coin (20 mm across) against the screen and adjust until the outline on screen matches exactly. Skip this and ring sizes can be off by 20–30%.
- 2
Choose a distance and measure it with a tape measure
Measure the chosen distance from the screen to your eyes with a tape measure. Marking the spot on the floor with masking tape lets you test from the same place next time. Pacing it out or judging by eye easily puts you 10–20 cm off.
- 3
Make the room and screen bright
Turn on the room lights and raise the screen brightness. Switch off night mode (blue light filter) and dark mode. Position the screen so windows and lights aren't reflected in it.
- 4
Cover the other eye with your palm
If you start with the right eye, gently cover the left eye with your palm. Cup it rather than pressing, and make sure you can't see between your fingers. After each eye, also measure with both eyes open.
- 5
Answer which way the gap faces
Answer whether the ring's gap is up, down, left or right using the buttons, a swipe or the arrow keys. If you can't tell, press "Can't tell" rather than guessing. Get 3 out of 5 right at one size to move to the next smaller step; get 3 wrong and the test ends.
- 6
Record the results for the right eye, left eye and both eyes
The last step you passed is that eye's acuity. Note "corrected" if you wore glasses and "unaided" if you didn't. Recording the date and distance too lets you compare next time.
Why online eye tests drift, and 7 tips for accurate measurement
"The app said 1.5, but the eye clinic said 1.0" is a common story. Most of the drift in screen-based tests comes from how the test is done. Follow these 7 points and the difference from a clinic result usually stays within 1–2 steps.
- (1) Calibrate the screen size: some sites just say "hold your phone 1 m away" without calibrating, but screens range from around 5 inches to nearly 7. Calibrating once with a card or coin removes most of the error.
- (2) Measure the distance with a tape measure: ring size is proportional to distance, so if you meant 2 m but sit at 1.8 m, your result comes out about 10% better.
- (3) Don't squint: squinting creates a pinhole effect that temporarily sharpens vision even for people with short-sightedness or astigmatism. That's why eye clinics tell you not to squint.
- (4) Don't press on the other eye: an eye that's been pressed hard looks blurry for a while. That's why the left eye can come out worse when tested after the right.
- (5) Don't memorise the answers: looking at the same chart layout repeatedly lets you remember the directions. Screen tests randomise the direction every time, which makes them harder to memorise than a paper chart.
- (6) Keep brightness and contrast the same: a dark room, dark screen or yellow-tinted screen can make results 0.1–0.3 worse. Testing at the same brightness each time makes comparisons with last time easier.
- (7) Test when you're not tired: after long periods on a phone or computer, the focusing muscles tire and acuity temporarily drops. Testing in the morning or after a break is best.
Reading your result: what 1.0, 0.7 and 0.3 mean
In Japan's decimal acuity, being able to see a 1.5 mm gap at 5 m is 1.0, only managing at twice that size is 0.5, and needing ten times the size is 0.1. Halving the number means the smallest size you can distinguish doubles. Here's what that looks like in daily life.
| Acuity | What you can see (rough guide) | Related standards |
|---|---|---|
| 1.0 or better | Can comfortably read the blackboard from the back row of a classroom | School grade A |
| 0.7–0.9 | Daily life is mostly fine, but small distant writing is hard to read | School grade B; ordinary driving licence needs 0.7 with both eyes |
| 0.3–0.6 | Hard to read the blackboard or TV text without moving closer | School grade C; ordinary driving licence needs 0.3 in each eye |
| 0.1–0.2 | Hard to recognise faces a few metres away | School grade D |
| Below 0.1 | Daily life is often difficult without glasses or contacts | — |
To compare your result with Japan's driving licence standards, see driving licence eyesight standards: 0.7 for an ordinary licence, 0.3 per eye, and checking at home before renewal; if you're curious about your child's school grade, see grades A, B, C and D in school eye tests. Results written as 20/20 or logMAR can be converted to Japanese decimal figures with what 20/20 vision is in Japanese acuity: a conversion table.
Check close-up vision (near acuity) and astigmatism too
Even with 1.0 distance vision, presbyopia, where fine print up close gets harder to read, starts after your 40s. Testing at 30 cm gives a guide to how well you see at phone or book reading distance (near acuity). At 30 cm, the gap in the 1.0 ring is a very thin 0.09 mm, and some screens can only draw down to about 0.7, so a printed chart is the reliable option there.
You can check for astigmatism by looking at a radial chart like a clock face, one eye at a time. If all the lines look equally dark, you have little astigmatism; if lines in one direction look darker and sharper, you probably have some. Multiply the smaller clock number at the ends of the darker line by 30 to get the approximate axis of the astigmatism (the rule of 30). For example, if the horizontal line from 3 to 9 o'clock looks darker, it's 3 × 30 = 90 degrees; if the vertical line from 12 to 6 o'clock looks darker, it's 6 × 30 = 180 degrees. This can't tell you the strength, so if you're concerned, have it measured at an eye clinic or optician.
See an eye doctor before testing at home if…
- Your vision has suddenly got worse, or changed in only one eye
- Lines look distorted, or there's a dark gap where you're trying to look
- Black dots or thread-like floaters have suddenly increased, or you see flashes of light
- You have eye pain, redness, or headache or nausea along with it
- There's a difference of 2 steps or more between your eyes, or you can't reach 0.7 even with glasses
- Your child squints, sits close to the TV or closes one eye to look
These signs matter more than any acuity number. They can point to conditions that should be treated quickly, such as retinal detachment or an acute glaucoma attack. Think of home testing as a tool for noticing changes early, and if you notice a worrying change, don't hesitate to see a doctor.
FAQ
- How far away should my phone be for an eye test?
- 1–2 m is recommended. If you calibrate the screen size and the rings are drawn to suit the distance, even 1 m gives the same test as a 5 m chart. At 5 m, the large 0.1 ring (over 7 cm across) won't fit on a phone screen.
- Are online and app eye tests accurate?
- If the screen size and distance are right, the rings are the same size as on a clinic's chart. But brightness and contrast conditions differ, so results can be off by about 0.1–0.2. Tests that don't calibrate the screen size can be 20–30% off depending on the device, so be careful.
- How should I cover one eye?
- Cup your palm like a bowl and cover the eye lightly without pressing. If you press hard, that eye will look blurry when you test it next. Also check that you can't see between your fingers.
- Can I test with my glasses on?
- Yes. Acuity with glasses or contacts is called corrected acuity, and without them, unaided acuity. Japan's driving licence standards accept corrected acuity, so if you're checking for your licence, test with the glasses you normally drive in.
- Does eyesight change during the day?
- It does. It can drop temporarily in the evening when your eyes are tired, or after long periods looking at a phone. To compare with last time, test at the same time of day, with the same brightness and at the same distance.
Tools in this article
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