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Astigmatism test (clock dial chart)
A quick astigmatism check using the clock-dial chart. See whether some line directions look darker or sharper than others, eye by eye.
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A screening aid, not a diagnosis. Screens, lighting and distance affect results. If something looks wrong, or your vision changes suddenly, see an eye-care professional. Medical disclaimer
How the chart works
The chart has groups of lines pointing in every direction, like the hours on a clock. An eye without astigmatism focuses all directions equally, so every group looks equally black. An eye with astigmatism focuses one direction better than the one at right angles to it, so some groups look darker, sharper or thicker.
Try it first without glasses. If you wear glasses that correct astigmatism, the lines should look even when you put them back on.
Limits of a screen check
Small amounts of astigmatism may not show on a screen, and the result depends on distance and screen sharpness. An eye exam measures astigmatism precisely, including its strength (the CYL number on a prescription) and direction (the AXIS).
Treatment
Astigmatism is corrected with glasses, toric soft contact lenses, rigid gas-permeable lenses, or laser procedures such as LASIK, PRK and SMILE. During cataract surgery, a toric lens implant can correct it too.
Questions people ask
What causes astigmatism?
Usually a cornea shaped more like a rugby ball than a basketball, so light focuses differently in different directions. It is often present from birth and is very common.
Can astigmatism get worse?
It can change slowly over time. A rapid increase, especially in teens and young adults, can be a sign of keratoconus and should be checked.
Do I need glasses for mild astigmatism?
Not always. Small amounts may cause no symptoms. If you have blur, eye strain or headaches, correction usually helps.