How to do the astigmatism test
- Sit or stand with the screen at arm's length on a phone, or about 2–3 metres (6–10 feet) from a laptop or TV screen. Use good, even lighting and turn the screen brightness up.
- Cover your left eye with your palm (do not press on it) and look at the red dot in the centre of the clock dial with your right eye.
- Without moving your eye, notice whether any of the lines look darker, blacker or sharper than the others. Tap those lines, or press All lines look the same.
- Repeat with the other eye covered. You then get a result for each eye, which you can share or save.
What is astigmatism?
Astigmatism means the front surface of the eye (the cornea) or the lens is shaped more like a rugby ball than a football, so it focuses light more strongly in one direction than another. Lines running in one direction then look sharp while those at right angles look blurred and lighter. It is very common: around a third of people have some astigmatism, often together with short- or long-sightedness, and most cases are mild.
The clock dial (also called a fan or sunburst chart) is a classic screening chart used by optometrists. With an even focus, all spokes look the same. If one spoke, or a pair next to each other, stands out, astigmatism is likely, and the direction hints at its axis: by the "rule of 30", the lower clock number of the darkest line multiplied by 30 gives the approximate axis of the correcting cylinder. An eye test measures it precisely.
A screen test cannot replace an eye examination. Your screen, the viewing distance, tiredness and dry eyes all affect what you see, and the test cannot detect other conditions. If you have sudden changes in vision, eye pain, flashes or floaters, see an eye doctor promptly.
What does it mean if some lines look darker?
That your eye focuses better in one direction than another, which is the main sign of astigmatism. Book an eye test to measure it.
Should I wear my glasses for the test?
Take it without glasses to screen your eyes, or with them to check whether your current prescription corrects astigmatism well.
Can astigmatism be corrected?
Yes. Glasses or toric contact lenses correct it, and laser surgery can treat many cases.
Is the online astigmatism test accurate?
It is a reasonable screening aid for noticeable astigmatism, but it can miss mild cases and give false alarms. Only a professional eye exam is accurate.