Look at a fan of lines and mark the ones that stand out. It's a classic screening exercise — it can't diagnose anything, but it can tell you whether a proper eye exam is worth booking.
Sit about arm's length from the screen and keep your glasses or contacts on. Cover one eye, look at the dot in the middle, and tap every line that looks darker, sharper, or bolder than the rest. Then switch eyes.
No lines marked for this eye. If they all look equally black and sharp, that's the typical result — though it doesn't fully rule astigmatism out. Mild cases can hide at home, because the eye's own focusing compensates for them — something an optometrist neutralizes with special lenses during an exam.
How to take the test
Keep your glasses or contacts on — the test should reflect how you actually see day to day.
Sit about an arm's length from the screen, in decent light.
Cover your left eye with your palm, without pressing, and select Right eye above the chart.
Look at the dot in the middle and tap every line that looks blacker or sharper than the rest — as if it were printed with more ink. If they all look the same, mark nothing.
Switch: cover your right eye, select Left eye, and repeat.
Arm's length matters. At a normal reading distance your eyes are focusing hard up close, which can change how the lines look. Sit back until your outstretched arm would just reach the screen.
Try it both ways. Run the test with your glasses or contacts on, then without. If some lines still stand out with your correction on, your current prescription may not be fully correcting the astigmatism — worth mentioning at your next exam.
What your result means
All the lines look the same: that's the typical result. This fan test looks for one specific sign of astigmatism — some directions appearing darker or blurrier than others — and your eyes didn't show it. It doesn't rule astigmatism out completely (mild cases often go unnoticed), but nothing here suggests you need to rush to get checked.
Some lines stand out: when a group of lines consistently looks darker or sharper, it can mean your eye focuses better in one direction than another — which is what astigmatism is. The test reports the rough direction of those lines only as context: it is not the axis an optometrist would put on a prescription, because measuring that takes proper instruments and a refraction exam.
Either way, an online screen can't replace an eye exam. Treat this result as a nudge, not a verdict.
Why a screen test is limited: your eye's own focusing can mask part of the effect, viewing distance at home is approximate, and every monitor renders lines a little differently. An exam room controls all three — which is why the same fan chart means more there than in a browser.
This is a screening exercise, not a medical test. It cannot diagnose astigmatism or any other condition, and its result is not a prescription value. If lines keep looking uneven, if your vision has changed, or if you get headaches or eye strain, book an exam with an optometrist or ophthalmologist.
What is astigmatism?
Astigmatism is a common focusing error. In an eye without it, the cornea — the clear front surface — curves evenly, like a slice of a sphere, so light comes to a single focus on the retina. With astigmatism, the cornea (or sometimes the lens inside the eye) curves more steeply in one direction than the other, closer to the back of a spoon. Light then focuses at two different points, and vision looks blurred or stretched at every distance.
That direction-dependent blur is exactly what a fan chart probes: lines lying along the eye's better-focused direction look crisp, while lines along the worse direction look grey or smeared. It's also why astigmatism appears on a prescription as two numbers — a cylinder power (how much correction is needed) and an axis (which direction it sits at).
Astigmatism is usually straightforward to correct with glasses or toric contact lenses, and in some cases refractive surgery is an option an eye doctor can assess. Most people have at least a small amount, and small amounts often need no correction at all.
Buying glasses online? You'll need your PD too
If an exam ends in a prescription, ordering glasses online takes one more number: your pupillary distance (PD). Our free tool measures it right in your browser with your camera — nothing is uploaded, nothing is stored.