Astigmatism

Astigmatism is a vision disorder that is mainly caused by an abnormality in the curvature of the cornea, the most anterior structure of the eyeball, which takes on a slightly more ovoid shape instead of a spherical one. This means that the light rays are not all focused on the same point on the retina, resulting in double vision and blurred images.
It can therefore be said that, in general, those suffering from astigmatism see objects that are poorly defined and, in severe cases, even slightly distorted: this visual defect is present in both near and far vision.

Astigmatism is measured in dioptres and is classified into: mild astigmatism (if it needs correction from 0 to 1 dioptre), medium astigmatism (from 1 to 2 dioptres) and severe astigmatism (over 2 dioptres). This vision defect is often associated with other visual disorders, such as hypermetropia, myopia or presbyopia.

Unless properly treated, astigmatism can cause certain disorders that result from constantly changing focus (accommodation) in an attempt to obtain a sharp image. These related symptoms are: eyeball pain, eye fatigue, burning eyes, headache and excessive tearing. 

As far as causes are concerned, astigmatism is usually caused by hereditary factors, but it may also occur as a result of trauma, injury or special surgery.            
There are also corneal diseases in which progressive astigmatism is only one of the most important signs. Keratoconus, for example, is characterised by an abnormal and progressive alteration not only of the curvature, but also of the structure and thickness of an area of the cornea. This leads to a more or less rapidly evolving astigmatism that requires specific investigations and treatment, up to and including, in the most serious cases, a corneal transplant.

In general, the easiest way to prevent astigmatism is to have regular eye examinations as early as 4-5 years of age, or even earlier if there is already a family history of astigmatism or eye disease.