About this visual acuity test
This is a real tumbling-E eye chart that runs in your browser — and unlike most online eye tests, the letters are rendered true-to-size. A 20/20 optotype is defined by physics: the whole letter subtends 5 arc-minutes of visual angle, and its critical detail — the thickness of each prong and the gap between them — subtends one. That one arc-minute is what your eye is actually resolving. To honor that on your screen, you first calibrate with any bank card (a globally standard 85.6 mm wide), which tells us your display's true pixels-per-millimeter. Combined with your viewing distance, every E is drawn at a genuinely correct visual angle.
You identify which way each E's prongs point, one eye at a time, down a level ladder from 20/200 toward 20/16. Wear your usual glasses or contacts — the result reflects your corrected vision. Two honest limits apply: very small optotypes hit your screen's pixel floor at close range (we compute and show that limit rather than fake it), and this estimates functional sharpness — it is not a refraction and cannot produce a prescription.
Frequently asked questions
Can you test visual acuity online accurately?
A useful estimate, yes — if letters are calibrated to real size (we use a credit card) and your distance is known. It's not a clinical exam or a prescription.
Why do I need a credit card for the eye test?
Screens vary in pixel density, so a card — a standard 85.6 mm everywhere — acts as a ruler to make the letters true-to-size at your screen's real scale.
What is the tumbling E test?
An eye chart of the letter E rotated four ways; you report the direction. It measures acuity with no reading needed, so it works for any language or young children.
Does this replace an eye exam?
No — it estimates current sharpness at a set distance, but can't refract, detect disease, or prescribe. A surprising result is a reason to book an exam.