How the astigmatism test works
The chart looks like a clock face. Twelve groups of three parallel black lines point from the center to every hour from 1 to 12, so the chart covers six directions 30° apart: 1–7, 2–8, 3–9 (horizontal), 4–10, 5–11 and 6–12 (vertical). The lines are all the same thickness and the same black. An eye that focuses evenly sees them all equally dark. This is a different check from the eye test, which measures how small a letter you can read.
The test has three short steps:
- Glasses or lenses. Tell the test whether you are wearing them. It is worth doing the test once without and once with your usual correction.
- Right eye. Cover your left eye with your palm, without pressing, and look at the dot in the middle. Choose All lines look equally dark and sharp, Some lines look darker or sharper or All lines look blurry. If some lines are darker, pick the pair of clock numbers at their ends, for example 3–9.
- Left eye. The same with the right eye covered.
Sit about an arm's length (50–70 cm) from the screen, turn the brightness up and keep your eyes on the center dot. Scanning the lines one by one makes them all look sharp in turn.
Each eye is tested on its own because the two can differ. Which eye your brain prefers when you line something up is a separate question, answered by the dominant eye test.
Why some lines look darker
Astigmatism means the front of the eye, the cornea, or the lens inside it is curved more steeply in one direction than in the one at a right angle to it, a bit like the back of a spoon instead of a ball. Light from one point no longer comes to one focus. Instead it forms two focal lines at different depths. Lines on the chart that run along one of those directions land in focus and look crisp and black; lines at a right angle to them are spread out and look grey, thinner or fuzzy.
That is why eye care professionals use a clock dial (also called a fan chart) during a subjective refraction: the direction of the darkest lines relates to the axis of the astigmatism, and they adjust a cylindrical lens until all lines look equal. This online test borrows the idea but does not measure the axis or the power. It only asks whether the lines look even.
Reading your result
- No sign of astigmatism on the chart – all lines looked equally dark to both eyes. A small amount of astigmatism does not always show on a chart like this, so this is not a guarantee.
- Possible astigmatism – lines in one direction looked darker to one or both eyes. The card shows the pair you picked for each eye, for example 3–9 (horizontal). If you did the test without your glasses or lenses, repeat it with them on. If the lines still look uneven with your current correction, the prescription may not fully cover the astigmatism.
- The lines looked blurry – every line was blurry. That usually points to short- or long-sightedness, the viewing distance or tired eyes rather than to astigmatism alone. The visual acuity test is a useful next step.
How common is astigmatism?
Very common. A meta-analysis by Hashemi and colleagues (2018) estimated that about 40% of adults and about 15% of children worldwide have some degree of astigmatism. Most of it is mild and present from birth. Many people never notice it, while others get blur at all distances, eye strain, headaches after reading or screen work, or glare and halos around lights at night.
Correction options
Mild astigmatism often needs no correction. When it does, glasses with a cylindrical lens, toric contact lenses or, for some adults, laser eye surgery can correct it. An exam measures both the power and the axis, so the lens is turned to exactly the right angle. Lenses from a simple ready-made reading glass do not correct astigmatism.
Limits of an online chart
The chart cannot measure dioptres or the axis. Screen size, distance, brightness and how well you hold your gaze on the center change what you see. If your glasses are smudged or your eyes are tired, the lines can look uneven for reasons that have nothing to do with astigmatism. If faint, low-contrast objects are what bother you, the contrast sensitivity test looks at that instead. Treat the result as a reason to look closer, not as an answer.
When to see an eye doctor
Book an eye exam if the lines look uneven on repeated tries, if you get frequent headaches or eye strain, or if your vision is blurry at both near and far. Go soon if your astigmatism or glasses prescription keeps changing quickly, especially in teenagers and young adults, because a progressive thinning of the cornea called keratoconus can show up this way. See a doctor the same day if your vision changes suddenly, if you see double with one eye, or if your eye hurts or is red.
More checks like this are collected on our vision tests page.
Sources
- Hashemi, H., Fotouhi, A., Yekta, A., Pakzad, R., Ostadimoghaddam, H., & Khabazkhoob, M. (2018). Global and regional estimates of prevalence of refractive errors: Systematic review and meta-analysis. Journal of Current Ophthalmology, 30(1), 3–22.
Frequently asked questions
Can I check for astigmatism online?
You can check for a sign of it. On a clock-dial chart, lines in one direction often look darker to an eye with astigmatism. Only an eye exam can measure its power and axis.
Which lines look darker with astigmatism?
It depends on the axis of your astigmatism. Lines along one direction look crisp and black, while lines at a right angle look grey or fuzzy. The test records the pair of clock numbers you pick for each eye.
Should I take the test with my glasses on?
Do it both ways. Without correction it shows whether you have uneven focus. With your glasses or lenses it shows whether your current prescription evens out the lines.
Why should I test each eye separately?
Astigmatism often differs between the two eyes. With both eyes open, the better eye can hide what the other one sees.
Can astigmatism go away?
Astigmatism present from birth usually stays fairly stable in adults. It can change with age, after eye surgery or with conditions such as keratoconus. Glasses, toric contact lenses or laser surgery can correct it.
All lines look blurry. Does that mean astigmatism?
Not necessarily. When every line is blurry, short- or long-sightedness, the distance from the screen or tired eyes are common causes. Try the visual acuity test and book an eye exam if the blur stays.