If you have astigmatism, you will also see auras
Curvature of the cornea (astigmatism)
As astigmatism, also astigmatism or astigmatism is a Refractive errors of the eye, in which the light rays are not bundled on one point of the retina, but on a line (focal line). The planes of incidence have different refractive power - a plane of maximum refractive power and one of minimum refractive power can be found. These are at right angles to each other. A stronger curvature leads to a greater refractive power, a smaller curvature to a lower refractive power. The difference in refractive power denotes the strength of astigmatism.
In the case of a normal-sighted eye, the incident light forms a point focus on the retina (left). If the cornea is curvature, it is rod-shaped (right)
The opposite is true for the corneal radius. A smaller radius is associated with a greater curvature and therefore with a greater refractive power and vice versa. The strength can also be described as the difference between the two corneal radii. The degree of astigmatism is given in dioptres (dpt.), Whereby 0.5 dioptres correspond approximately to a radius difference of 0.1 millimeters.
According to the rule and against the rule
In most cases, the cornea is more curved in the vertical axis than in the horizontal axis - one speaks of astigmatism according to the rule. If the opposite is true and the cornea is more curved in the horizontal axis, it is a curvature of the cornea contrary to the rule.
Regular and irregular astigmatism
The name of the curvature of the cornea is very similar, but with reference to the position of the curved planes in relation to one another. The most common form of this visual defect is the regular form.
Symptoms of astigmatism
While there are different forms, the common symptoms of astigmatism are astigmatism blurred and / or blurred vision. The items may also be distorted. The symptoms are independent of whether an object is viewed near or far. Slight forms of astuteness are often not perceived at all.
A typical symptom of astigmatism is distorted or blurred vision.
As a result of the blurring, there is pain in the eyes and burning eyes due to the constant focus of the eyes. Headaches from constant exertion and strained vision are also not uncommon.
Causes of astigmatism
The most common cause of astigmatism is one congenital deviation of the cornea from the circular shape. Muscular problems of the eye muscles, differences in density within the layers of the lens or very high myopia could be considered as rare causes. After surgical interventions such as squint operations or surgical procedures for glaucoma or cataracts, the cornea can also be curved differently due to scarring.
Normal astigmatism is determined by the eye doctor or optician using the autorefractometer when determining the eyesight. An ophthalmometer or keratograph is used for a more precise determination. With this, two luminous images are projected onto the cornea, which are reflected on it. The mirrored images are made congruent in the device and then the radius of curvature must be read off. This makes it possible to determine the strength of the curvature and whether the cornea is curved uniformly or irregularly.
With the help of special images (astigmatism sun gear) or the Snellen ray figure you can get an impression for yourself:
The astigmatism sun wheel: With healthy eyes you can see all rays equally sharply (left). In the case of astigmatism, opposing pairs of rays look blurred (right).
If you can see all the rays and distances on the sun gear equally sharply, then there is no pronounced astigmatism. If the cornea is curved, the opposing rays look different in one direction than the perpendicular pairs of rays. If the image is rotated, the direction in relation to the eye remains the same. The fuzzy pairs of rays do not rotate with the image.
With the corneal topography, the surface of the cornea can finally be measured even more precisely and the structure can be displayed. The result is an image of mountains and valleys on the surface of the cornea - similar to a map.
What treatment or therapy options are there?
The correct therapy is based on the present form. There are various options for correction:
glasses: With glasses with cylinder lenses - so-called toric or sphero-toric lenses, curvatures up to a certain strength can be compensated. These are spectacle lenses that correct an axial position, for example myopia, and compensate for the curvature of the cornea perpendicular to it.
contact lenses: Due to the tear film between the contact lens and the surface of the cornea, irregular curvatures of the cornea can be compensated to a certain extent with dimensionally stable contact lenses. Correction can also be made with soft contact lenses, which align themselves on the crooked cornea due to the asymmetrical weight distribution.
Laser astigmatism: The surface of the cornea can be smoothed by the ablation with a laser and thus an astigmatism correction can be carried out. This is a method that has been used for over 25 years and can be performed quickly and painlessly.
Lens replacement: If the shape is very pronounced, the lens of the eye can also be replaced. The cornea remains in the originally curved shape and the artificial, new lens is shaped accordingly in order to compensate for the curvature of the cornea as best as possible.
Corneal transplant: In very rare cases it is not possible to achieve a sufficient correction using any of the options mentioned. The last resort is to transplant a non-curved donor cornea.
To correct a curvature of the cornea, the cylinder (1) and axis (2) values are required.
Information on the glasses prescription
Corrections cannot be made by specifying the strength in dioptres (dpt.). Further values must therefore be specified: The type of correction is specified in cylinder (cyl.) And the position based on the axis position in degrees. A vision of up to 0.5 diopters is considered normal and does not require any correction. This value arises from the deviation of the cornea from the ideal shape of the circle.
Course of the disease and prognosis
Even if astuteness is a rather complicated visual defect, it usually remains constant and does not worsen. A congenital, higher-grade astigmatism, however, can lead to irreversible, functional visual impairment in children if not treated in good time.
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