Astigmatism In The Population, With-the-rule astigmatism, Against-the-rule astigmatism, Oblique astigmatism, Regular astigmatism, Irregular astigmatism, Astigmatism is an unevenness of the cornea where instead of the cornea being round it is more oval so a good way to think about it is with looking at a dessert or a soup spoon. So a soup spoon is where the cornea is round and has no astigmatism. But if you look at a dessert spoon it is more oval than round What are the different types of corneal astigmatism? Well corneal astigmatism is delineated from 0 to 30 and 150 to 180 degrees as against the rule, then you have 30 to 60 and 120 to 150 degrees being oblique, leaving the 60to 120 degrees being with the rule and with the rule is more of a favourable orientation. What percentage of people have a significant amount of astigmatism? Significant astigmatism of 1D or greater can be found in more than 36% of people. Surgically the aim is to leave patients with less than 0.50D of astigmatism.