What are astigmatism and myopia
The eyeball of a myopic eye is too long to focus the incoming rays exactly on the center of the retina and thus create a sharp image.
The refraction of light on the cornea and lens results in a sharp image only in front of the retina - the distance between the center of the retina and the lens system of the eye is too great. The correction is carried out with diverging lenses, which move the point of impact of the light rays to the center of the retina, i.e. backwards.
The eyeball of a hyperopic eye is too short to focus the incoming rays exactly on the center of the retina and thus create a sharp image.
The refraction of light on the cornea and lens results in a sharp image only behind the retina - the distance between the center of the retina and the lens system of the eye is too small. The correction is carried out with converging lenses that move the point of impact of the light rays to the center of the retina, i.e. forwards.
In the case of astigmatism, curvatures of the cornea lead to different degrees of refraction of the incident rays, so that their image does not appear as a point on the retina, but is drawn out in the shape of a rod. This creates blurred and distorted images on the center of the retina.
Astigmatism can occur independently of other ametropia or in combination with them. The correction is carried out with cylindrical lenses that bundle the differently refracted rays and unite them again into one point.
The lens of the eye has the ability to adjust to different distances and thus produce sharp images on the retina in the distance and near. This ability is lost with age.
From around the age of 40, it becomes more difficult to quickly produce sharp images for different distances, and seeing close up and on the screen becomes more strenuous and diminishes. Presbyopia is therefore not a disruption of the length of the eyeball, but is due to the decreasing mobility of the lens of the eye. Correction is carried out with reading glasses or lenses.
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