Astigmatism: the defect that blurs vision at every distance

Astigmatism, along with myopia and hyperopia, is a refractive error an optical condition in which images are not correctly focused on the retina. Its distinctive feature is that the defect concerns the very shape of the cornea, the transparent window covering the eye: instead of being perfectly spherical like a soccer ball, the astigmatic cornea is slightly oval, like a rugby ball, and focuses light rays on different planes depending on their direction.

The result is that a point of light is not perceived as a sharp point, but as a small line or a doubled image. This is why, unlike myopia, astigmatism tends to blur vision both at a distance and up close, fairly consistently at every distance.

Comparison between the vision of a normal eye and an astigmatic eye: the image appears doubled.

How common it is

Astigmatism is extremely common, and in its mild form it is almost the norm: roughly speaking, a very large proportion of the population has some degree of astigmatism, often so slight that it requires no correction at all. It is frequently accompanied by myopia or hyperopia, and is largely a trait one is born with, stable over time.

Symptoms

Typically, a patient with uncorrected astigmatism reports slightly “smeared” or doubled vision, a tendency to squint to bring things into focus, and, above all, visual fatigue with headaches after prolonged reading or driving. In children, high uncorrected astigmatism can hinder the normal development of vision, which is one of the reasons why an eye exam at preschool age is so valuable.

Corneal topography maps the curvature of the cornea and reveals its irregularities.

Regular and irregular astigmatism

Broadly speaking, two situations must be distinguished. Regular astigmatism, by far the most common, depends on the natural shape of the cornea and is easily corrected with appropriate lenses. Irregular astigmatism, on the other hand, arises from a corneal surface deformed by a disease — in particular keratoconus, a progressive bulging of the cornea — or by a scar, and requires dedicated solutions. This is why astigmatism that increases rapidly, especially in a young person, always deserves further investigation.

How it is corrected

In everyday life, regular astigmatism is corrected with glasses fitted with toric lenses — lenses with different curvatures along different axes — or with specific contact lenses. In adulthood, once the defect is stable, it can be permanently corrected with laser refractive surgery (PRK, femto-LASIK, SMILE), which reshapes the cornea, restoring a more regular geometry. Astigmatism can also be corrected during cataract surgery, by choosing a toric intraocular lens.

In conclusion

In its common form, astigmatism is a thoroughly manageable travel companion: an appropriate correction is enough to restore sharp vision at every distance. However, precisely because irregular forms linked to corneal diseases do exist, worsening astigmatism should not be dismissed as simply needing a change of glasses. A comprehensive eye exam including corneal topography clarifies the nature of the defect and points, case by case, to the safest solution.