Eye Test

How to take the online eye test

1. Open Calibrate to your screen and match a bank card (or enter your screen size). Without this the letters are the wrong size and the score is meaningless.
2. Choose the distance you will sit or stand from the screen and measure it with a tape: 3 m (10 ft) or more on a computer or TV, 40 cm on a phone. Use Full screen for the far distances.
3. Keep your glasses or contact lenses on if you wear them for distance. Cover your left eye with your palm (do not press) and press Start with Right eye selected.
4. For each E, press the arrow for the way its arms point, on the keyboard or the buttons. A helper can press for you. If you cannot tell, press Can't tell; do not lean closer.
5. The test moves to a smaller line after three right answers and stops after three wrong answers on one line. Then pick Left eye, cover your right eye and repeat.

What the results mean

Your score is the smallest line you got at least three out of five right on, written the way an optometrist writes it:

If the page says or better (screen limit), your screen did not have enough pixels to draw the smaller lines at that distance. Step further back, choose the longer distance and test again. On a phone at 40 cm the test checks near vision, which is different from distance vision.

How the letter size is worked out

Visual acuity charts are built on one rule: a letter on the 20/20 line is 5 minutes of arc tall at the viewing distance (one twelfth of a degree), and each stroke and gap of the E is 1 minute of arc. At 6 m (20 ft) that is 8.7 mm; at 3 m it is 4.4 mm; at 40 cm it is 0.58 mm. A 20/40 letter is twice that size, 20/200 ten times. The page works out each size from your distance and your screen calibration and draws the E on exact pixels.

The tumbling E is used for children and people who do not read the Latin alphabet, and it cannot be guessed from the letter shape. Letter mode shows a classic chart with rows of letters for reading aloud to a helper; it uses a standard bold font rather than the official Sloan letters, so treat it as a quick check and use the E test for a score.

What an online eye test cannot do

A chart checks one thing: how sharp your vision is at one distance. A full eye examination also measures your exact prescription, checks eye pressure, looks at the retina and optic nerve, and tests eye movement, depth perception and the visual field. Many eye diseases, including glaucoma and early diabetic eye disease, cause no blur until late. Have a full eye examination every two years (every year for children, people over 60 and people with diabetes), even when an online test looks fine.

See a doctor straight away for sudden loss of vision, a curtain or shadow over your vision, new floaters with flashes of light, double vision, or a painful red eye.

Common problems and fixes

The letters look too big or too small

Calibrate with a bank card and keep browser zoom at 100% (Ctrl+0 or Cmd+0). Measure the distance from your eyes to the screen with a tape, not by guessing.

I cannot reach the keyboard from 3 metres

Ask a helper to press the arrows while you call out the direction, use a wireless keyboard, or use the phone setting at 40 cm.

The smallest lines are skipped

Your screen does not have enough pixels for them at this distance. Move further away and choose the longer distance, or use a screen with a higher resolution.

My result is worse than at the optician

Screen glare, low brightness, a dirty screen, tired eyes or the wrong distance all lower the score. Test in a well lit room with the screen at full brightness.