Astigmatism is a condition in which the transparent structure of the front and / or back surface of the eye – the cornea – does not have a perfect spherical shape. This creates an optical defect, which is the refraction of light rays with different strengths. This means that only part of the object in question is in focus. Things in the distance may look blurred .
Vision with astigmatism
Often astigmatism is combined with nearsightedness or farsightedness. All of these conditions are refractive abnormalities because they involve a disturbance of light refraction.
Astigmatism can be corrected quite well with properly fitting glasses, soft contact lenses, and laser surgery.
Symptoms of astigmatism
Patients often complain of discomfort during prolonged visual work, headaches, a feeling of tension in the eyes, and mainly a distorted image.
Most people are born with this condition. But also, it can appear after traumatic injury to the eye, eye diseases and surgical treatment.
In rare cases, the appearance of astigmatism is caused by keratoconus. This is a condition in which the cornea becomes thin and takes on a conical elongated shape.
In order to diagnose astigmatism, the following tests are performed:
Autorefractometry-determination of the refraction of the eye using infrared light. This is a routine method that is performed at every eye exam.
Keratometry – allows determining the curvature in the central zone of the cornea.
Examination on a phoropter. The phoropter is an automated device that has many lenses in it. The ophthalmologist changes a series of lenses in order to determine the most appropriate lens to improve vision.
Keratotopography. This examination provides the most complete view of the cornea. The topographer automatically creates a color “map” of the cornea.
Rules of eyeglasses selection
After a thorough ophthalmologic examination, the ophthalmologist begins to select the corrective eyeglasses.
In order for the glasses for astigmatism to be comfortable and contribute to the maximum visual acuity, it is important to perform control tests. These tests make sure that the correction is chosen correctly.
Initially, the ophthalmologist is guided by the data obtained through autorefractometry. A lens of a certain strength is placed in the trial frame on a certain axis. The ophthalmologist then performs a cross-cylinder test, which allows determining the lens power to an accuracy of 0.25 diopters and determining the lens axis to 1 degree.
The prescription for eyeglasses for each eye indicates the value of the spherical lens when nearsightedness or farsightedness is present and the cylindrical lens when astigmatism is present. At the end of the line the value of the axis on which the cylindrical lens is placed is marked.
Below indicates the interpupillary distance and the purpose of the spectacle correction (for distance, for reading, for computer work). It is worth noting that it is recommended to wear glasses for astigmatism at all times.