Measurement and Topography Guided Treatment of Irregular Astigmatism

Corneal astigmatism occurs when one corneal meridian has a different refractive power from the orthogonal meridian. In regular astigmatism, the two meridians are at 90o from each other, such as a sphere having a cylinder superimposed on its surface. In irregular astigmatism the two meridians are not at 90o from each other or the cornea curvature is not axially symmetric. Irregular astigmatism can be imagined as a sphere, with or without a cylinder on its surface, and several other different shapes superimposed on it. In irregular astigmatism the same meridian has different degrees of curvature, making it impossible for a spherocylindrical lens to correct such irregularity. (1) The diagnosis of irregular astigmatism can be suspected when there is loss of spectacle corrected visual acuity but preservation of vision through pinhole or while wearing rigid gas-permeable contact lenses. Other clues for the presence of irregular astigmatism are difficulty in determining the axis of astigmatism during manifest refraction, a significant amount of astigmatism at automated refraction not accepted by the patient and achieving the same visual acuity despite correction of the cylinder in different axis. Patients complain of bad quality of vision resulting from glare, halos, distortion of image and monocular diplopia. The diagnosis can be confirmed with a topographic examination.