Astigmatism Test
Look at a clock dial of radiating lines: if some look darker or sharper, astigmatism may be present.
Astigmatism is a common refractive error in which the front surface of the eye (the cornea) or the lens is curved more steeply in one direction than in the other, more like a rugby ball than a football. As a result, light is not focused at one point, and lines in some orientations look sharper than lines in others. Mild astigmatism is very common and often needs no correction; larger amounts can cause blur at all distances, eye strain and headaches.
This tool shows a classic astigmatic dial, also called a clock dial or fan chart: groups of lines radiating from the centre like the hours on a clock. With no significant astigmatism, all lines look equally black and sharp. With astigmatism, one or more directions may look darker, bolder or crisper while the lines at a right angle to them look greyer or fuzzier. The position of the darkest lines roughly relates to the axis of the astigmatism.
The dial is a quick screening aid. It cannot measure how much astigmatism you have, and it can miss small amounts, especially if your eye compensates by focusing. Only a refraction by an optometrist or ophthalmologist can quantify astigmatism, and progressive, irregular astigmatism (for example in keratoconus) needs specialist tests.
How to use
- Sit about 50 cm to 1 metre from the screen in good lighting.
- Remove your glasses for a first check, then repeat with them on to see whether your correction balances the lines.
- Cover one eye with your palm without pressing.
- Look at the centre of the dial for a few seconds without squinting.
- Notice whether all lines look equally dark and sharp, or whether some directions stand out.
- Note the 'clock hours' of any lines that look darker, then repeat with the other eye.
Reading your result
If all lines look the same in each eye, there is no sign of significant astigmatism on this check. If one set of lines consistently looks darker or sharper, astigmatism may be present in that eye. Differences that change every time you blink or that disappear with your glasses on are less likely to matter.
Book an eye examination if the effect is clear without glasses and you have symptoms such as blurred or doubled edges, eye strain, headaches or trouble driving at night, or if the effect persists even with your current glasses, which may mean your prescription needs updating. Rapidly changing astigmatism, especially in teenagers and young adults, should be checked for keratoconus.
Caution: Screening only, not a diagnosis or prescription. It does not measure the amount or exact axis of astigmatism. See an eye doctor for any sudden change in vision.
Frequently asked questions
Can eye exercises correct astigmatism?
No. Astigmatism comes from the shape of the cornea or lens, and exercises cannot change that shape. Glasses, contact lenses or refractive surgery correct it.
Is a little astigmatism normal?
Yes. Small amounts are found in most people and often cause no symptoms. Whether to correct it depends on your vision and comfort.
Why do the darker lines change when I tilt my head?
Astigmatism has a direction (axis) fixed to the eye. When you tilt your head, the eye turns with it, so the darker lines appear in a different position on the dial.