Corneal curvature-Astigmatism
Astigmatism is a visual disorder related with changing curvature of the cornea.
The cornea in the human eye has flat and horizontal curvatures which are fully adapted to each other.
These curvatures receive direct light as well as light coming from the sides.
However, the light entering through the pupil is reflected differently if the corneal curvature is more or less curved to one side and is dissolved in different meridians. For example, an round object, like a sphere, is perceived as a line or stick.
Astigmatism causes to symptoms including headache, blurred vision, sensitivity to light and blinking. Astigmatism is divided into two groups: regular and irregular astigmatism.
Astigmatism is divided in 5 groups according to the optic localization:
1. Simple hypermetropic astigmatism: one meridian is emmetropic and the other one is hypermetropic.
2. Simple myopic astigmatism: One meridian is emmetropic and the other one is myopic.
3. Combined hypermetropic astigmatism: Both meridians are hypermetropic, though with different degrees.
4. Combined myopic astigmatism: Both meridians are myopic, though with different degrees.
5. Mixed astigmatism: One meridian is hypermetropic and the other one is myopic.
Regular astigmatism may be corrected with cylindric eyeglasses. In cases of irregular astigmatism, a few focusing lines are observed instead of the regular lines mentioned above.