Having astigmatism: definition, symptoms and correction

Having astigmatism means having an eye whose cornea or lens is not perfectly spherical, but slightly oval, like a rugby ball. Light does not converge on a single point on the retina: the image is blurred or distorted at every distance, both up close and far away. It is a very common refractive error, correctable with glasses, contact lenses or surgery.

UNDERSTANDING

What is an astigmatic eye?

An eye is described as astigmatic when its optical surface — mainly the cornea, sometimes the lens — does not have the same curvature along every axis. In an emmetropic eye (with no refractive error), the cornea is regular and rounded like a football. In a person with astigmatism, it is slightly more curved in one direction and flatter in another, much like a spoon or a rugby ball.

This is known as corneal toricity. Because the curvature varies from one axis to another, the light entering the eye does not converge on a single point on the retina, but on two distinct focal lines. The brain receives an image that is doubled or stretched in a specific direction — which explains the particular sensation of blur, present whatever the distance of the object being viewed.

Astigmatism is a very common refractive error, in the same way as short-sightedness or long-sightedness. Most people have a slight degree of it, often with no effect on daily life. It is only when it becomes significant that it disturbs vision and warrants correction. Its measurement is expressed in dioptres, together with an axis in degrees.

SYMPTOMS

What are the symptoms of astigmatism?

The most characteristic symptom of astigmatism is blurred or distorted vision at every distance, both up close and far away. Unlike a short-sighted person who sees poorly at a distance and well up close, someone with astigmatism perceives a constant blur, often accompanied by an impression of doubling of outlines and letters.

Constant blur and doubled outlines

Many people with astigmatism describe lines that seem slightly tilted, letters that resemble and blend into one another (the “E” and the “F”, the “8” and the “0”), or outlines that appear to bleed. The blur is not uniform: it shows up mainly in one direction, that of the most distorted axis of the cornea. This asymmetry of vision can make long spells of reading exhausting.

Halos, glare and night-time discomfort

At night, when the pupil dilates, the optical error becomes more noticeable. People with astigmatism frequently see halos around light sources: car headlights, street lamps, traffic lights. Night-time driving can become uncomfortable, with characteristic glare and streaks of light.

Eye strain and headaches

To compensate for the blur, the astigmatic eye constantly strains to regain sharpness. This sustained accommodative effort leads to eye strain (asthenopia), especially at the end of the day or after prolonged screen work. Headaches, stinging eyes and the need to squint are common. In children, uncorrected astigmatism can show up as reading difficulties or reduced concentration at school.

THE TWO FORMS

Regular or irregular astigmatism: what is the difference?

Two main families of astigmatism are distinguished according to the shape of the cornea. This distinction has direct consequences for how it is corrected.

Regular astigmatism

In regular astigmatism, the deformation follows two well-defined perpendicular axes: a most curved meridian and a flattest meridian. It is the most common form, often present from birth and stable over time. Correction with a cylindrical (toric) lens is generally enough to restore clear vision. Regular astigmatism can be corrected with glasses, toric contact lenses, and most often with refractive surgery.

Irregular astigmatism

Irregular astigmatism corresponds to a disorganised corneal surface, with no clear axis or symmetry. It can result from a corneal scar, an injury, previous surgery, or a progressive deformation such as keratoconus. This type of astigmatism is more difficult to correct with simple glasses and often requires custom rigid lenses, or even a specialist ophthalmic assessment before surgery is considered.

ASSOCIATED ERRORS

Can you have astigmatism and be short-sighted, long-sighted or presbyopic at the same time?

Yes, and it is in fact very common. Astigmatism frequently combines with another refractive error. This is known as associated visual errors: each anomaly adds up, which explains sometimes mixed symptoms and a prescription with several figures. The combined visual errors page details these associations and their implications for correction.

• Astigmatic and short-sighted: the distance blur of short-sightedness is compounded by distortion at every distance. This is the most common combination, often corrected with a spherocylindrical lens.
• Astigmatic and long-sighted: the effort to see up close is increased by the astigmatism, with marked eye strain, especially during prolonged reading.
• Astigmatic and presbyopic: after the age of 45, the difficulty seeing up close linked to presbyopia is added to the astigmatic blur; progressive lenses then incorporate all three corrections.

In every case, the ophthalmic prescription specifies each component: the sphere for short-sightedness or long-sightedness, the cylinder and axis for astigmatism, the addition for presbyopia. Understanding the logic of these figures helps you communicate better with your ophthalmologist and live comfortably with your correction.

MEASUREMENT

How is astigmatism measured?

The diagnosis of astigmatism is based on a complete, non-invasive and quick eye examination. The ophthalmologist measures the refraction of the eye, then analyses the shape of the cornea. These measurements make it possible to quantify the astigmatism, identify its axis and determine its nature.

Refraction and reading the prescription

Refraction assesses the optical power of the eye and the error to be corrected. An automatic device (refractometer) gives a first estimate, refined by the subjective examination: the practitioner has letters read through different lenses until optimal sharpness is achieved. The astigmatic dial — a wheel-spoke drawing — helps identify the least sharp axis. On the prescription, the cylinder (marked C or CYL) expresses the intensity of the astigmatism in dioptres, together with the axis in degrees (0° to 180°).

Corneal topography

Corneal topography maps the surface of the cornea point by point and produces a colour map of its curvatures. It distinguishes regular astigmatism from irregular astigmatism, and screens for possible anomalies such as keratoconus. It is an essential examination before any surgical correction is considered: it determines whether the cornea has the thickness and regularity needed for laser ablation.

CORRECTION

How is astigmatism corrected?

Having astigmatism is by no means inevitable: the error is well corrected day to day. Depending on the degree of astigmatism, lifestyle and expectations, several solutions exist, from glasses to surgery.

Glasses with toric lenses

Glasses with toric lenses (or cylindrical lenses) remain the simplest and best-tolerated solution. The lens is ground to compensate for both the sphere (short-sightedness or long-sightedness) and the cylinder (astigmatism), according to the precise axis of the cornea. They are suitable for every degree of astigmatism, whether regular or moderately irregular.

Toric contact lenses

Toric lenses — soft or rigid — offer an alternative for those who prefer not to wear glasses. Fitting them is more delicate than standard spherical lenses, because the lens must remain precisely oriented on the eye. In cases of marked irregular astigmatism (keratoconus, scarring), custom rigid lenses or scleral lenses may be necessary.

Refractive surgery: LASIK, PRK, SMILE, toric implants

For people who wish to free themselves lastingly from glasses and contact lenses, refractive surgery can treat astigmatism directly on the cornea or inside the eye:

• LASIK and PRK use an excimer laser to reshape the cornea and correct astigmatism up to around ±5 dioptres, provided the cornea is thick enough.
• SMILE cuts a corneal lenticule with a femtosecond laser and can treat myopia-astigmatism within similar ranges.
• When the cornea is too thin or the error too great for a laser, a toric phakic implant (toric ICL) can be placed inside the eye to correct both short-sightedness and astigmatism.

This page is intended as a definition and a guide. The detailed surgical indications, eligibility criteria and expected results are presented on the astigmatism correction page. Eligibility for surgery is determined during a complete pre-operative assessment.

FREQUENTLY ASKED QUESTIONS

Frequently asked questions about astigmatism

Sources

• French Society of Ophthalmology (SFO) — Refraction and refractive errors: definitions, astigmatism, short-sightedness, long-sightedness and their management.
• College of University Ophthalmologists of France (COUF) — Item “Refractive errors”: regular and irregular astigmatism, corneal topography, keratoconus.
• French National Authority for Health (HAS) — Recommendations on the correction of refractive errors and laser refractive surgery.

This article is intended for information purposes and does not replace a medical consultation. Only an eye examination can measure your astigmatism, establish a personalised diagnosis and discuss the correction options suited to your situation.