Short answer
Almost everyone has a little astigmatism. It becomes worth correcting when it starts to blur or stretch what you see — most often noticed when driving at night, or as glasses that never feel quite sharp.
What is astigmatism?
A healthy cornea is curved the same amount in every direction, like a football. With astigmatism it is curved more steeply in one direction than the other, like a rugby ball lying on its side.
That explanation is accurate and it stops where your actual questions begin. It does not tell you how to read the cylinder on your own prescription, why headlights streak at night, what astigmatism looks like in a child who has never complained, or when a stretched image is pointing at something else. That is the rest of this page.
What it actually looks like
- Letters that look stretched or doubled rather than foggy
- Street lights and headlights with streaks or starbursts at night
- Squinting, which briefly sharpens things and is why people do it
- Tired eyes and headaches after reading or screen work
- Vision that is nearly right with glasses but never quite crisp
Night driving is the complaint we hear most. An uncorrected cylinder turns every oncoming headlight into a smear, and the effort of resolving it is tiring in a way people rarely connect to their eyes.
How to read your prescription
| SPH | Short or long sight. Minus is short-sighted, plus is long-sighted. |
| CYL | How much astigmatism. The cylinder. |
| AXIS | Which direction it runs, from 1 to 180 degrees. Not a strength — a compass bearing. |
A worked example. If your right eye reads −2.50 / −0.75 × 180, that is 2.50 dioptres of short sight, 0.75 of astigmatism, running horizontally. The axis on its own tells you nothing about how much there is; it only tells the lab which way to orient the lens.
How much is a little, how much is a lot?
| up to 0.75 | Mild. Common. Many people never notice it. |
| 0.75 to 2.00 | Moderate. Usually worth correcting, especially for driving. |
| above 2.00 | Strong. Correction makes an obvious difference. |
These are guides, not thresholds. Someone with 0.50 who drives at night may notice more than someone with 1.50 who does not.
What causes it?
Mostly the shape you were born with. Astigmatism runs in families and is usually present from childhood. It is not caused by reading in dim light, sitting close to a screen, or any of the other things people are told.
It can also come from the lens inside the eye rather than the cornea, which is less common. More rarely it follows an eye injury, surgery, or a thinning of the cornea called keratoconus, where the astigmatism is irregular and changes over time. That last one matters, because it is one of the findings that rules a laser procedure out.
Astigmatism in children
Children almost never complain about blurred vision, because they have nothing to compare it to. What you see instead is behaviour: sitting very close to the screen, losing the line when reading, tilting the head to one side, avoiding reading, or headaches late in the day.
Why a good examiner may not prescribe glasses straight away
Between 30 and 50 per cent of infants have significant astigmatism. Not a trace of it — the mixed kind, with a plus sphere and a strong cylinder. On a prescription slip it looks alarming.
It also has a consistent direction. The axis sits close to 180, the pattern called with-the-rule astigmatism: the cornea is steeper in the vertical meridian than the horizontal one. As above, the axis is a compass bearing and not a strength — a reading of 180 says nothing about how much astigmatism there is, only which way it is oriented.
That consistency is a clue in itself. A refractive error that turns up in a third to a half of all infants, pointing the same way in nearly all of them, is not a collection of individual faults. It is something happening to eyes as a group.
One explanation is simple mechanics: during development in the womb the eyelids press on a soft, still-growing eye, and the eye takes on the shape it is pressed into. Press from above and below and you get an eye steeper in that direction — which is exactly what with-the-rule astigmatism is.
That shape does not usually last. As the eyeball and the rest of the body grow, the cornea rounds out and most of this early astigmatism disappears on its own. The eye is running a process called emmetropization — actively tuning itself towards a focus that works.
It takes its time. The tuning runs until roughly the age of six to eight. That sets the expectation: this is not a question answered at one follow-up appointment. It is a measurement repeated over several years while the eye finishes its own work.
Which leads to something that surprises parents. An experienced paediatric ophthalmologist or optometrist will often choose to observe and re-examine rather than prescribe glasses the first time astigmatism is found in a small child. Not out of caution about the cost or the fuss, but because a lens placed in front of an eye that is still tuning itself can interfere with the tuning. Correcting too early can hold in place the very error that was on its way out.
So an early appointment is not a step towards glasses. It is a measurement and a date to come back — and for most small children, repeated over those years, that is the whole treatment.
What the follow-up is for is the minority where the astigmatism does not fade, or where one eye is markedly different from the other. Those are the cases where vision in the weaker eye can fall behind, and where the window for doing something about it does not stay open indefinitely. Telling those two groups apart is what the repeat examination does.
How it is measured
With a map of the cornea. An autorefractor gives a first estimate, the optometrist refines it by lens comparison, and corneal topography measures the surface point by point and draws it as a colour map. The map is what shows whether the astigmatism is regular — the ordinary kind a lens corrects — or irregular, which points at something else.
How it is corrected
Those are the options in general. Here is what they mean at this clinic.
Glasses
The simplest answer and the right one for most people. A cylindrical lens bends light more in one direction than the other, cancelling out the shape of the eye. A first pair at a new cylinder can feel odd for a day or two — floors may seem to tilt — and that settles.
Contact lenses
Astigmatism needs a toric lens, which has to stay oriented the right way round on the eye rather than rotating freely. They work well for most people. Long days in them tend to be drier, which is worth knowing if you already have dry eye.
Laser correction
A laser reshapes the cornea so it refracts evenly, which removes the cylinder rather than compensating for it. At KSA the Flow3 procedure is for people aged 18 to 45 whose short-sightedness has been confirmed at an examination; astigmatism is corrected along with it. If you are long-sighted, outside that age range, or not sure what your prescription is, the route starts with an Audit eye examination instead — that is also the examination that finds the reasons a procedure would not be a good idea. Recovery takes about a week, with sport and swimming once the bandage lenses come out.
We do not implant lenses inside the eye for astigmatism. Where that is the right answer, we say so and refer.
Does it get worse?
It changes slowly, if at all. Most people’s astigmatism is fairly stable through adulthood, with small shifts over years. A noticeable change over months is worth looking at rather than waiting out, because that pattern is more typical of keratoconus than of ordinary astigmatism.
Coming from Finland
Tallinn is about two hours from Helsinki by ferry, and the clinic is a short ride from the harbour. Examinations and procedures are carried out in English. Most people plan one trip for the examination and a second for the procedure itself.
What to do next
If you have a prescription with a CYL on it and your vision is good with glasses, nothing needs doing. If night driving is tiring, if glasses never feel quite sharp, or if you are wondering whether the cylinder can be removed rather than corrected, book an eye examination. It takes about an hour and you leave with the measurements, whatever you decide afterwards.
We examine in Tallinn and in Tartu. The laser procedure itself is done in Tallinn.