If you have blurred vision both at a distance and at close range, the cause may be a so-called astigmatism. The eye is no longer able to focus the incident light on an exact point on the retina and thus to bring it into focus, but the affected persons see points as blurred lines. Normally, the cornea of the eye is almost spherically curved in both horizontal and vertical directions, so that light coming in from the side as well as from the front enters the eye. However, when this natural corneal curvature deviates from its normal shape in astigmatism, the refractive power of the eye changes.
Definition Astigmatism
By definition, astigmatism is an eye defect caused by astigmatism. The curvature of the cornea causes an aberration in the eye’s optical system, resulting in blurred vision near and far, depending on the degree of astigmatism. The word “astigmatism” has its origins in Greek and means “pointlessness”. Due to the astigmatism of the cornea, incoming rays of light do not hit the retina in one point, but in a line or rod shape (hence the German term “Stabsichtigkeit”).
Forms of astigmatism
Depending on the type of astigmatism present, a distinction is made here between different forms: Regular astigmatism is the curvature of the cornea when there is unequal refractive power in two perpendicular planes (meridians). – If the refractive power is stronger in the vertical plane than in the horizontal plane, one speaks of astigmatism according to the rule. – If the refractive power is stronger in the horizontal plane than in the vertical plane, one speaks of astigmatism against the rule. Irregular astigmatism occurs when the refractive power differs greatly at different points on the cornea.
- Regular astigmatism (regular astigmatism):
- Irregular astigmatism (irregular astigmatism):
Causes
Astigmatism of the eye is caused by astigmatism of the cornea, which can have various causes. In rare cases, astigmatism is not only caused by the cornea, but also by other parts of the eye that also contribute to the refractive power of the eye (e.g. the lens of the eye). Regular astigmatism Most often, the cause of regular astigmatism is hereditary.
Since birth, people with astigmatism see through a curved cornea and thus the typical regular or regular astigmatism develops. In this form, the refractive power is differently pronounced in two perpendicular planes. According to science, this form of astigmatism changes only insignificantly in the course of life.
Irregular astigmatism An astigmatism with irregular astigmatism and thus irregularly distributed refractive power of the eye is called irregular astigmatism. The causes of this can be corneal scars or corneal ulcers, so that the refractive power is very different at different points due to the different curvatures of the cornea of the eye. However, irregular astigmatism can also be caused by an irregularly curved or clouded lens, such as in cataracts.
Irregular astigmatism can also occur as a result of a so-called keratoconus. This is a malformation of the cornea so that the cornea grows conically outwards in the middle. This results in operations that are necessary again and again and the cornea becomes thinner and thinner and scarred in the course of the disease. Irregular astigmatism can also be caused by surgical procedures, in which a temporary scarring of the cornea of the eye occurs, but then recedes again. This is the case, for example, after surgery for glaucoma or cataract.
