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.
Have you caught yourself driving at night thinking that oncoming headlights and streetlamps are no longer clean points of light, but elongated streaks, starbursts or distracting halos? Or that letters on a screen or a page look slightly doubled, stretched downwards or shadowed, even though your glasses ought to be right?
If that sounds familiar, it is nothing unusual. In Estonia this is often called "cylinder vision" in everyday speech; the medical name is astigmatism. It is not a disease and not an inflammation, but an ordinary optical focusing error. Almost everyone has a mild degree of it. When it starts to interfere with daily life, to tire the eyes or to cause headaches, it needs accurate assessment and correction.
What astigmatism is and why it happens
The simplest way to understand what is going on inside the eye is to picture two sports balls.
In a well-focused eye the clear front window — the cornea — is evenly curved in every direction, shaped like a round football. Light rays passing through such a cornea bend equally in every meridian and converge to a single sharp point on the retina. The result is a sharp, high-contrast image.
In an eye with astigmatism the cornea is unevenly curved, more like a rugby ball lying on its side. Because the cornea is steeper in one direction and flatter in the other, light rays do not bend the same way along every meridian. Instead of converging to one point, the light spreads across several focal lines. The brain receives an image that is sharper in one direction and out of focus in the other — and that is what shows up as stretched, blurred or doubled vision, both near and far.
Besides corneal astigmatism, which is the most common form, there is also lenticular astigmatism, where the uneven curvature lies in the lens inside the eye rather than in the cornea. The optical consequence is the same in both: light scatters and never forms a single sharp image on the retina. Astigmatism coming from the lens is rarer, and it shows up when the keratometry values are read.
Signs worth not ignoring
Astigmatism does not always present as obvious blurriness. People often adapt over years without noticing the gradual loss of visual quality. There are, however, specific signs.
- Tiring, distracting night drivingIn the dark the pupil is dilated. A wider pupil uses more of the cornea and amplifies the unevenness of its curvature. Headlights and illuminated signs turn into streaked bursts or spreading beams of light. It is the complaint heard most often in eye clinics.
- Stretched or doubled lettersReading a book or a screen, letters can look elongated at the top or bottom, as though the text had a shadow under it.
- Constant squinting and early wrinkles around the eyesSquinting works like narrowing a camera aperture: it restricts the light coming in and sharpens the image for a moment. Constantly tensing the muscles around the eye brings on wrinkles early.
- Eye strain and headachesWhen the eye muscles work continuously to focus an unclear image, the day ends in fatigue, dryness and a tension headache across the brow.
- Glasses that are almost clear, but never quite sharpIf a prescription is missing the cylinder it needs, or has it slightly wrong, the image can be better than without glasses yet never crisp.
How to read your prescription
If you have had an eye examination, your prescription carries three main values.
- SPH — sphere
- Short-sightedness (a minus sign) or long-sightedness (a plus sign), in dioptres.
- CYL — cylinder
- The strength of the astigmatism in dioptres: how much extra bending power is needed to compensate for the oval shape of the cornea.
- AXIS
- The direction of the astigmatism in degrees, from 1 to 180. The axis is the compass bearing along which the correcting lens must be oriented — not the strength of the cylinder.
Example. If the right eye reads −2.50 / −0.75 × 180°, that is 2.50 dioptres of short-sightedness and 0.75 dioptres of astigmatism, with the correcting axis at 180 degrees, which is horizontal.
Mild, moderate and strong
- Up to 0.75 dioptresMild. Very common. Many people pay it no attention day to day, though it can make itself felt driving at night.
- 0.75 to 2.0 dioptresModerate. Usually worth correcting, so that reading is comfortable and driving is safe.
- Above 2.0 dioptresStrong. Correction makes a clear difference between sharp and out-of-focus vision.
There are exceptions. Someone with 0.50 of astigmatism who often drives at night may notice their cylinder more than someone with 1.50 who never drives.
Astigmatism in children, and why a specialist may not prescribe at once
Children almost never complain of blurred vision, because they have nothing to compare it with — they assume the world looks like this. Parents notice habits instead: the child sits very close to the screen, tilts their head while reading, loses their place on the line, avoids reading, or has headaches in the evening.
Why an experienced examiner may not prescribe glasses straight away
Between 40 and 50 per cent of infants are born with significant astigmatism. It is usually mixed: a spherical plus prescription with a strong regular astigmatism on top of it. On the refractometer both the plus figures and the astigmatism figures can therefore look surprisingly large.
The reason is simple. During fetal development the eyelids press on a soft, still growing eyeball. Because they press from above and below, the cornea becomes steeper in the vertical meridian than in the horizontal. This is called with-the-rule astigmatism, and the axis sits close to 180 degrees.
As the eye grows, a natural process called emmetropization takes place. The eyeball and the facial bones grow, the eyelids become more elastic, and the eye actively tunes itself towards a more accurate focus. The cornea rounds out on its own and most of that early infant astigmatism simply grows out, by roughly the age of six to eight. The process can be documented at annual vision checks.
And out of this comes a fact that often surprises parents. At first detection an experienced paediatric ophthalmologist or optometrist will frequently choose observation and a repeat examination over writing a prescription. Not to save money or to create extra work, but because a spectacle lens in front of an eye that is still tuning itself can disturb emmetropization or stop it altogether. Correcting too early can lock in exactly the error that was on its way out.
So an early vision check is not a step towards glasses. It is measurement and monitoring, and in most small children that is the whole of the treatment. Glasses are prescribed when the astigmatism is unusually strong, does not reduce over time, or when the refraction of the two eyes differs markedly — the last of these can lead to a lazy eye, amblyopia. Telling those two groups apart is the job of an experienced optometrist or ophthalmologist.
What causes astigmatism, and how it changes over a lifetime
Contrary to a widespread myth, astigmatism is not caused by reading in dim light, sitting close to the television or working at a computer.
- Heredity and the shape you were born withThe shape of the cornea is mostly inherited. Astigmatism runs in families and is usually present from birth.
- Natural change with ageIn adulthood astigmatism is mostly stable. In younger people the axis is typically close to 180 degrees, while over the age of fifty it can shift towards 90 degrees as the lens inside the eye changes.
- A warning sign: rapid change over monthsIf the astigmatism changes markedly over a few months rather than years, it needs checking. A rapidly increasing, irregular astigmatism can point to a corneal disease called keratoconus — the cornea stretching and thinning — or to the consequences of an injury. Finding keratoconus matters, because it rules out the usual laser procedures.
How astigmatism is diagnosed
Autorefraction gives only a first, general picture of the eye's refractive power. For an accurate diagnosis and a safe correction, clinics use corneal topography — mapping the cornea.
A topographer measures the corneal surface at thousands of separate points and builds a detailed three-dimensional colour map from them. The map shows the thickness, curvature and flatness of the cornea to within a micron. It is what distinguishes two things:
- Regular astigmatismThe cornea is evenly oval, rugby-ball shaped. It can be corrected with glasses, contact lenses or laser.
- Irregular astigmatismThe corneal surface is uneven or scarred. That points to a disease such as keratoconus and calls for specialist solutions.
Ways of correcting astigmatism
Glasses · cylindrical lenses
The lens bends light more in one plane than the other, balancing out the oval shape of the eye.
Advantage. Simple, safe, non-surgical.
Limitation. The first few days may need adaptation — the floor can look slightly tilted. Limits an active lifestyle.
Toric contact lenses · a lens that stays oriented
A specially weighted lens that holds its position on the eye instead of rotating freely.
Advantage. A wide field of view and the freedom to play sport.
Limitation. Long days tend to dry the eye. They need daily care and hygiene.
Lenses inside the eye · IOL
A toric artificial lens is placed in the eye, either in addition to your own lens or in place of it.
Advantage. Comes into consideration for a very strong astigmatism.
Limitation. This is eye surgery, with the risks that surgery carries.
Laser correction · KSA Flow3
The laser reshapes the surface of the cornea to a more even curve, removing the astigmatism along with the short-sightedness.
Advantage. A permanent result, touch-free and blade-free.
Limitation. Needs a stable prescription and a thorough pre-examination. Flow3 is for confirmed myopes aged 18 to 45.
A permanent solution at KSA: touch-free, blade-free Flow3
When glasses and contact lenses tire you or limit an active life, one answer is laser vision correction. At KSA Vision Clinic the astigmatism is corrected together with the short-sightedness in the Flow3 procedure. Flow3 is for people aged 18 to 45 whose myopia has been confirmed at a suitability examination.
- Entirely touch-free and blade-freeUnlike older-generation LASIK methods, Flow3 cuts no flap in the cornea and uses no mechanical blades. The laser works without contact, directly on the surface layer of the cornea.
- The structure of the cornea is preservedBecause no incisions are made into the cornea, the biomechanical strength of the eye is retained.
- RecoveryThe procedure itself takes a few minutes. Sport, training and swimming are possible 7 days afterwards, once the bandage lenses have been removed. Fuller recovery takes a few weeks.
- Experience and guaranteeKSA Vision Clinic has been operating since 2005 and has carried out more than 300,000 eye examinations. Thanks to a strict pre-screening protocol there has not been a single case of corneal weakening, ectasia, in that time. Depending on the package, the procedure carries a guarantee of up to 10 years.
The first step: a Vision Audit examination
The route to clear vision starts with a thorough diagnosis. The Vision Audit is a comprehensive examination in Tallinn and Tartu, in which optometrists and ophthalmologists assess corneal thickness, three-dimensional topography and intraocular pressure, and establish whether your astigmatism is regular and suitable for a laser procedure.
We examine in Tallinn and in Tartu. The laser procedure itself is done in Tallinn, because that is where the laser is.