Astigmatism

In astigmatism, the cornea, instead of having a spherical type conformation, may have different curvatures in some areas.

In practice, if we imagine the cornea crossed by many axes intersecting at the centre, we might find that not all axes have the same curvature.

Consequent to this we will have that all the image going to the retina will be normal but the part of the light crossing the axis with different curvature will arrive at the retina distorted either forward or backward to the retina.

The subject, therefore, perceives a more or less blurred image.

Astigmatism is corrected with appropriate lenses called cylindrical lenses, which are placed on the frame so that only the axis with the different curvature is corrected.