What is astigmatism ?
Astigmatism is most frequently associated with irregular curvature of the cornea (or, much more rarely, of the lens). The astigmatic cornea does not have the same radius of curvature in all meridians and presents two main radii, one of them more “arched” than the other. So it is that a single object is broken down into two images rather than one; while the first is in front, the second is behind; their positioning with regard to the retina determines whether the astigmatism is myopic, hyperopic or compound. The eye’s shape is closer to an oval than to a circle, and it bears more resemblance to a rugby ball than to a soccer ball.
The astigmatic eye yields distorted vision at all distances (near, far…), and at times entails eyestrain and headaches when reading.
Vision correction is carried out by means of opthalmic lenses or contact lenses characterized as sphero-cylindrical or toriodal, through which the two previously distinct images are merged and brought back onto the retina, as a single one.
The same effect can be achieved using laser by differentially modifying the two main radii of curvature.