What is the meaning of the numbers used to describe the degree of astigmatism?
Astigmatism is measured in diopters (D), a standard optical measure. In simple terms, the diopter represents the reciprocal of the focal distance in meters. For example, a patient with 2 D of nearsightedness would have a far focal point of ½ meter. A patient with ½ D would have a focal point 2 meters in the distance. In my experience, many patients have between 0.25 and 2.00 D of astigmatism. Between 2.25 and 3.75 is less common, but still seen. Much above that in a “normal” patient is unusual. Keratoconus and post-transplant patients can have 10D of astigmatism or even more.
