Online Vision Test
Quick check your visual acuity, astigmatism, and color perception on your smartphone or PC screen
Features
Start measuring instantly with no setup
Begin immediately by inferring screen resolution from your device type
Display at actual size by entering screen dimensions
Enter the diagonal screen size in inches to display the C-ring at the correct size for your device
Measure each eye separately
Test each eye individually and compare the difference in vision between left and right
Three types of checks: acuity, astigmatism, and color vision
Start each of the three checks independently from the initial screen
How to Use
Select the type of check
Choose from "Vision Test," "Astigmatism Check," or "Color Vision Check" on the initial screen
Enter screen size (optional)
Enter your screen's diagonal size in inches from the "Measure more accurately" option on the pre-test instructions
Step away from the screen and cover one eye
Stand at the instructed distance (50 cm or 1 m) from the screen and cover the designated eye with your hand
Answer questions about what you see
Use arrow buttons, arrow keys, or swipe to indicate the direction of the C-ring's opening. For astigmatism, select how the lines appear; for color vision, select the number you see
Check results for each eye
Review your results for each eye and any notes on the result screen. Choose "Test again" if needed
Use Cases
Confirm vision when you notice difficulty seeing
Quickly check your current vision on a smartphone or computer as a reference before visiting an eye doctor
Check for differences between your eyes
Compare results from your right and left eye to see if one eye is not seeing clearly
Estimate trends in astigmatism
Gauge whether you may have astigmatism by observing how radial lines appear
Confirm color perception
Read numbers hidden in colored dots to check if there are any colors you have difficulty distinguishing
Knowledge
What does 20/20 vision mean?
20/20 vision refers to the ability to distinguish the opening direction of a Landolt ring (C-shaped symbol) with an outer diameter of 7.5 mm and opening width of about 1.5 mm when viewed from 5 meters away.
- Visual angle of 1 minute：The opening of a 20/20 vision ring is designed so that the visual angle (the angle subtended from the eye) is 1 minute (1/60 of a degree).
- How decimal visual acuity is calculated：Decimal visual acuity is the reciprocal of the visual angle (in minutes) of the smallest opening that can be distinguished. A visual angle of 2 minutes equals 0.5 acuity, and 0.5 minutes equals 2.0 acuity.
Difference between decimal and 20/20 notation
Decimal notation is used in Japan and other countries, while 20/20 notation is used in the United States and other countries, based on a reference distance of 20 feet (approximately 6 meters).
- How to convert：In 20/20 notation, the denominator is 20 divided by decimal acuity. Decimal 0.5 equals 20/40, and decimal 2.0 equals 20/10.
- Meaning of the denominator：20/40 means that what a person with standard vision can distinguish at 40 feet, you can barely distinguish at 20 feet.
How reliable is smartphone vision testing?
Vision measured on a smartphone or computer is only an estimate based on the assumption that the symbol size displayed and the viewing distance are as expected, and cannot replace an eye examination by an optometrist.
- Effect of screen resolution：If the actual screen resolution differs from what is assumed, the displayed size of the C-ring changes, and your results may be higher or lower than your actual vision.
- Effect of viewing distance：Symbol size is determined based on viewing distance. If you view a display designed for 50 cm at 40 cm, your result will be higher than your actual vision.
- Upper limit of measurable vision：The opening cannot be rendered correctly once it becomes smaller than one pixel, so the upper limit of measurable vision decreases on devices with coarser screens.
Safety and Privacy
Runs entirely in your browser
Your input data is processed only within your browser and is never sent externally.
Processing only in your browser
Judgment of answers and calculation of results is processed entirely within your browser, and input data is not sent to any server.
Communications encrypted with HTTPS
Page loading is also encrypted by TLS, and content cannot be read by third parties.
No transmission to third parties
Input content is not sent to external services such as ad networks or trackers.
No automatic saving of results
Answers and measurement results and input suggestions are not stored on the server.
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Updates
- update #310
Added online vision test - check visual acuity, astigmatism, and color perception on smartphone and PC screens