How to use
- Sit about 1 m (3 ft) from a computer screen, or hold a phone about 40 cm (16 in) away.
- Cover your left eye, press Test right eye and look at the centre of the chart for a few seconds.
- If lines in some directions look darker or sharper, select them and confirm; if all look the same, press All look the same.
- Then test your left eye and read the results.
Options explained
- Clock directions
- The chart is numbered 1–12 like a clock, and each line is named by the hours at its two ends — the vertical line is 12–6, the horizontal line 3–9.
- Astigmatism
- The cornea or lens is curved more in one direction than another, so light focuses well in one direction and not in the other, and things blur along one direction.
Reading the chart
There are lines in six directions, three parallel lines each, all with the same width, colour and spacing. An eye without astigmatism sees every direction equally clearly. An eye with astigmatism focuses well in one direction and poorly at right angles to it, so one set of lines looks dark and crisp while the set at 90° looks grey with soft edges.
While you look:
- Use one eye. Cover the other gently with your palm without pressing on it.
- Don’t squint. Squinting temporarily hides astigmatism.
- Look at the centre for a few seconds. Your eye settles after a moment.
- Go with your first impression. Stare too long and every line starts to shimmer.
Astigmatism versus short- and long-sightedness
Short- and long-sightedness blur every direction at once; astigmatism blurs one direction more than the others. They often come together. If most directions looked fuzzy, overall short- or long-sightedness is more likely — check how far down you can read with the vision test.
When to get your eyes checked
- Letters look doubled or smeared, or lights at night have streaks.
- Reading or screen work quickly tires your eyes or gives you headaches.
- A child squints, tilts their head or holds things very close.
An optometrist or eye doctor can measure astigmatism, and glasses or contact lenses usually correct it. You can also check your colour vision with the colour blind test.
Frequently asked questions
No line looked darker. Does that mean no astigmatism?
It means no obvious astigmatism. Very mild astigmatism doesn't show on this chart; only an eye exam measures its amount and axis.
How does this relate to the axis on my prescription?
A rough rule is to take the smaller clock number at the ends of the darkest line and multiply by 30. If 2–8 looked darkest, the axis is near 60°. It is only an estimate; the eye exam is what counts.
Does astigmatism always need glasses?
No. Mild astigmatism is very common and many people never notice it. Double or smeared vision, tired eyes, streaks around lights at night, or a child who squints or tilts their head are reasons to get an eye exam.
Is it worth testing with my glasses on?
Yes. If one direction still looks darker with your glasses on, they may not fully correct your astigmatism — worth mentioning at your next check.
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