Guide · astigmatism
Astigmatism: what it is, how it feels, and how it is corrected
Astigmatism is one of the most common reasons people need glasses, and many people have a little without knowing. It is not an eye disease. It simply means the front of the eye is shaped slightly differently, and it is easily corrected.
What astigmatism is
A perfectly even eye is curved the same way in every direction, like a football. With astigmatism the front of the eye (the cornea), or the lens inside it, is curved a little more in one direction than the other, more like the back of a spoon. Light coming in is focused at two different points instead of one, so the picture is not quite sharp.
You can have astigmatism on its own, or together with short sight or long sight. It is usually there from birth and changes slowly, if at all.
How it feels
- Blur at all distances, near and far
- Lights that streak, flare or have halos, especially driving at night
- Letters that look smudged or doubled at the edges
- Squinting to see clearly, and tired eyes or headaches after reading or screens
A small amount often causes no symptoms at all. That is why it is usually found at an eye test rather than noticed.
How it is measured
At your eye test the optometrist measures how much astigmatism you have and at what angle, and checks the shape of the front of the eye. On your prescription it shows as the cylinder (CYL) and axis numbers. The axis is just the direction, from 0 to 180, not how strong it is.
How it is corrected
Glasses. A lens made stronger in one direction than the other cancels out the uneven curve. Most people adjust within a few days. Why new glasses can feel strange at first.
Contact lenses. Toric lenses are made to stay the right way round on the eye. Most people with astigmatism can wear them, including dailies. Contact lenses for astigmatism.
Laser surgery can reshape the cornea for some adults. We can tell you at your eye test whether your eyes are likely to suit it.
Does it get worse?
In most adults astigmatism stays much the same for years. A sudden change, or astigmatism that keeps increasing, is worth checking, because occasionally it is a sign of keratoconus, where the cornea gradually thins and changes shape. Keratoconus and scleral lenses.
Your next step
An eye test measures it exactly. Free on the NHS if you qualify, otherwise £55, and free when you buy your glasses with us.
The short version
- Astigmatism means the front of the eye is curved unevenly
- It blurs near and far, and makes lights streak at night
- It shows on your prescription as CYL and axis
- Glasses or toric contact lenses correct it
- A sudden change is worth checking