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Online visual acuity test (Sivtsev / Snellen chart)

An online visual acuity chart. For a meaningful result, the screen is first calibrated with a bank card, then you set the viewing distance — so the letters get the correct physical size. This is a self-check and a reference point; exact acuity is measured by an ophthalmologist on calibrated equipment.

Step 1. Screen calibration

Which eye

Why calibration is needed

Monitors and phones differ: the same "20-pixel letter" has a different physical size on each. Without a correction, an online chart is meaningless. So we ask you to hold a bank card to the screen (its width is standard — 85.6 mm) and fit a frame to it — that tells us how many pixels are in a millimetre on your screen.

The second key parameter is the viewing distance: acuity depends on the angle the optotype subtends. Once you set the distance, the letters get the correct size for each acuity row.

How to run the check

For an honest result:

  • calibrate the screen with a card and set the real viewing distance;
  • test each eye separately, covering the other with your palm (not squinting);
  • good even lighting, a clean screen, normal brightness;
  • if you wear glasses/lenses for distance — check both with and without them.

What the result means

Acuity 1.0 (written 20/20) is normal: you resolve the detail designed for a "standard" eye at your distance. Lower values (0.7, 0.5, etc.) mean reduced acuity — but the cause is often simple (fatigue, an uncalibrated screen, the wrong distance) and usually calls for an eye exam rather than worry.

An online check does not replace an exam: it does not measure refraction, does not check the retina and does not prescribe glasses. If you see worse than expected or your vision changed, see an ophthalmologist.

Frequently asked questions

  • Accurately — no: an online chart is a guide, not a diagnosis. But with screen calibration via a bank card and a set distance the result becomes meaningful — you can tell whether acuity is near normal. Exact acuity and refraction are measured by an ophthalmologist on calibrated equipment.

  • It is calibration: a card’s width is standard (85.6 mm by ISO), so fitting a frame to the card lets us compute how many pixels are in a millimetre on your screen. Without it the letters would have a random physical size and the test would be meaningless.

  • Acuity 1.0 is normal: the eye resolves the detail designed for standard acuity at the proper distance. "20/20" is the same in feet notation (you see at 20 ft what a normal eye sees at 20). 20/40 (0.5) means you see at 20 ft what a normal eye sees at 40.

  • Both are useful. Without correction you see your "raw" acuity; in glasses/lenses for distance — how well they correct. If acuity in your glasses is noticeably below 1.0, they may be outdated — see an ophthalmologist.

  • As a preliminary guide, yes: an online chart shows whether your acuity is close to the level required to drive. But the official check for a driving medical is done by an ophthalmologist on a standard chart with calibrated equipment — the online result does not replace it. It is worth checking at home in advance so there are no surprises at the exam.

  • Adults with no complaints — usually every 1–2 years, and more often after 40–45 or with risk factors (diabetes, hypertension, high myopia), on your ophthalmologist's advice. An online check can be run every few months for self-monitoring — handy for spotting a change in time and booking a visit.

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This check is for reference and is not diagnostics. An online chart does not measure refraction and does not replace an ophthalmologist’s exam. If your vision drops or changes, see a doctor.