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The effects and causes of astigmatism

The expressions short-sightedness and long-sightedness are understood by most people. This is different with astigmatism, also known as a corneal curvature. Behind this unusual word lies a widespread visual impairment that affects a large part of the population. If you would like to find out how this visual defect occurs and how it can be corrected, you will find what you are looking for here.

What is asigmatism?

For a sharp visual perception, the optical parts of the eye, such as the cornea and lens, bundle the incoming light in a normal functioning eye onto the retina in a dot-like manner. Most people are familiar with this effect of a converging lens of a magnifying glass. However, this only works if the surface of the cornea is symmetrical - like the circular section of a sphere. If, for example, the cornea has a different radius in the x-axis than in the y-axis and is oval in shape, there is a curvature of the cornea. As a result, light no longer coincides in a focal point. Instead, it forms so-called focal lines on the retina. Among other things, this results in dot-shaped objects appearing "blurred" - in the form of small bars. In contrast to short-sightedness or long-sightedness, astigmatism does not rely on distance.

Good to know: the cornea is not always the triggering factor in astigmatism, even if the common term "corneal curvature" suggests this. If the eye lens is incorrectly shaped, it is a so-called lens astigmatism, but this is much rarer.

What are the causes of astigmatism?

Astigmatism is generally hereditary. Similar to short-sightedness or long-sightedness, this is not noticeable in patients with mild variants: the brain automatically compensates the problem to a certain extent. The estimates regarding the distribution of astigmatism vary greatly: from about 20 to 40 %. Possible triggers for a severe corneal curvature are also corneal diseases and eye operations.

How can this visual impairment be corrected?

Luckily, correcting astigmatism is not a problem. A corneal curvature can be corrected on its own or together with another defective visual acuity. The latter is usually the norm. Glasses lenses and contact lenses with an asymmetrically curved surface (so-called toric contact lenses) are used to compensate for the irregular shape of the cornea. These are so-called cylindrical lenses, in the glasses pass indicated by the abbreviations "Zyl" or "Cyl". They have this name because on closer inspection their surface appears as if bent around a cylinder. These include prescription values for the amount of astigmatism in dioptres and the axis position in degrees, which indicates the orientation of the cylinder axis.

A correction of several visual impairments such as a combination of short-sightedness, presbyopia and astigmatism is nowadays not a problem. Modern varifocal lenses are available with a cylinder value and thus eliminate astigmatism. At the same time they offer the familiar high comfort and allow sharp vision at all distances.