If there is astuteness, the person concerned sees objects in the near and far out of focus. The cause is usually a curvature of the cornea

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Clarity - briefly explained

Astigmatism is a special visual disorder. Mostly, the different curvature of the cornea (corneal curvature) leads to errors in the image and thus distorted vision. The cause is less often in the area of ​​the lens, very rarely in the area of ​​the fundus. The astuteness is often associated with a farsightedness or nearsightedness. The causes of astuteness can be genetic, in these cases it is innate. However, scarring or certain diseases can also lead to astigmatism. The visual disturbance is diagnosed by examining the eye with special devices. There are different forms of astuteness. Depending on the shape, asthma is treated either with glasses with specially cut glasses or suitable contact lenses; in certain cases, operations with or without implants are also possible.

What is astuteness?

The astuteness is a visual disorder that is usually caused by an irregularly shaped cornea. If the cornea is curved to different degrees, the light rays falling into the eye (what is seen) are not bundled in one point on the retina. As a result, the person concerned sees objects near and far in a distorted or out of focus. Headaches and burning eyes can also appear as additional symptoms.

Schematic representation of the eye structure (here in the picture a "healthy" cornea)

© Fotolia / Vanessa

How does astuteness come about?

Usually the cornea bulges in a spherical shape and is equally curved in all directions. If light rays emanating from an object hit the cornea, they are also refracted evenly and bundled to a point on the retina. However, if the curvature of the cornea is irregular, it refracts the incoming light rays to different degrees. In this way, what is seen no longer creates a point on the retina, but instead a line or a rod - the image is distorted. Doctors therefore speak of astuteness.

Which forms of astuteness are differentiated?

Most often the cornea curves more vertically than horizontally. In this case there is astigmatism according to the rule. If the horizontal plane is more curved, it is an astigmatism against the rule.

Furthermore, ophthalmologists differentiate between regular and irregular astigmatism. In the former, the differently curved planes are perpendicular to one another. In the latter, the cornea is bent to different degrees in different places.

Causes: What leads to astuteness?

Astigmatism according to the rule is in most cases congenital and inherited. But there are also triggers that have nothing to do with genes:

  • For example, the cornea can curve irregularly if the upper eyelid presses too hard on it.
  • Scars (for example after surgery) and diseases can change the curvature of the cornea. With so-called keratoconus, the cornea bulges so much over time that it looks like a cone.
  • Corneal opacities, such as those found in cataracts, are sometimes also the cause.

A deformed cornea is not always the basis for astigmatism. The lens or the fundus of the eye can rarely be the trigger for astigmatism.

Symptoms: What symptoms does astuteness cause?

Those who are only slightly intent on staff often do not notice this at all. It is only noticeable when the visual impairment is more pronounced. Those affected then see blurred in the distance, but also close up. Objects can look either blurry or distorted.

Since the lens is constantly trying to focus on the distorted image, the muscles in the eyes are often tense. It is hard to see and pain in the eyes. People also often have headaches and stinging eyes. In many cases, people who are wands suffer from both myopia and farsightedness.

Normally, astuteness does not deteriorate. This means that those affected always see the same blurred.If one learns astuteness already in childhood, however, the eyesight can deteriorate over time.

Depiction of a placido disc

© iStock / w_inx

Diagnosis: How is astuteness determined?

The ophthalmologist can get a first impression with the help of the so-called Placido disk. There are several circles on it, which are arranged like a target. In the middle there is a small opening through which the ophthalmologist can look.

During the examination, the examiner approaches the patient with the Placido disk until the circles are reflected on the cornea. If the eye is healthy, the circles appear exactly as they do on the disk. If there is astigmatism, the mirror image looks rather oval. With the Placido lens, however, only a very pronounced astigmatism can be recognized.

The ophthalmologist can examine the corneal surface more precisely with an ophthalmometer. With this device he can measure whether the cornea curves evenly or irregularly. The doctor can also use it to determine how strong the astuteness is. The ophthalmometer projects two luminous images onto the cornea, which are reflected on it. The doctor adjusts the distance between the images until the reflections are exactly on top of each other. The expert then reads off the radius of curvature. This is repeated in different axes and the results compared.

The so-called corneal topography is even more precise. Here, the surface of the cornea is measured and the surface structure is made visible in the image - similar to a topographical map in which mountains and valleys are depicted.

Therapy: How is astuteness treated?

Which therapy is suitable depends on the type of astuteness that is present. Your doctor will discuss with you which method is best suited in each individual case, which advantages and disadvantages it has and whether the costs will be covered by the statutory health insurance.


If the astigmatism is regular (see colored extra box above), the vision problems can be compensated for with special glasses or contact lenses. Cylinder glasses are used here. These compensate for the wrong curvature by refracting incident light rays in such a way that they are displayed as points on the retina. To do this, the ophthalmologist or optician must first determine the refractive power of the eye and the visual acuity.

contact lenses

Contact lenses can also correct this form of astigmatism. Depending on how pronounced it is, the ophthalmologist will prescribe normal or toric lenses. Like the special lenses, the latter are cylindrically curved. Contact lenses have the disadvantage that they can cause corneal inflammation if they are not properly cared for and cleaned.

Glasses are not suitable for people who suffer from the irregular form of astigmatism. However, hard (dimensionally stable) contact lenses enable these patients to see clearly again.


The astuteness can also be treated surgically. Such an operation can compensate for the refractive error of the cornea (possibly also of the lens) and has the effect that the person concerned no longer perceives objects in a distorted manner. Ophthalmologists refer to these surgical procedures as refractive surgery. There are different methods that can be used to change the curvature of the cornea. Most often this procedure takes place with the help of a laser. The surgeon uses a laser to carefully remove the areas that are excessively curved so that the corneal surface is uniformly formed again.


More and more often, specialists are inserting additional lenses into the eye ("add-on lenses"). This procedure has the advantage that doctors have more experience with the procedure.

Prof. Dr. med. h.c. Arthur Mueller

© W & B / private

Our advisory expert:

Professor Dr. med. Dr. hc. Arthur Mueller is a specialist in ophthalmology and director of the clinic for ophthalmology at the Augsburg Clinic. He is a member of numerous specialist societies. His professional focus is on microsurgical interventions on the posterior (retina, choroid, vitreous humor) and anterior segment of the eye (cataract, glaucoma, keratoplasty).


  • Professional association of ophthalmologists in Germany, astigmatism. Online: (accessed on April 29, 2020)

Important note: This article contains general information only and should not be used for self-diagnosis or self-treatment. He can not substitute a visit at the doctor. Unfortunately, our experts cannot answer individual questions.