Astigmatism and Tissue-Shape Disparity in Penetrating Keratoplasty

Tissue-shape disparity between the donor and recipient cornea is a major cause of astigmatism following penetrating keratoplasty. We studied the topographic effects of recipient or donor tissue deficiency (oval donor button or recipient hole) in a penetrating keratoplasty rabbit model. The results demonstrated that a crescent-shape block resection of 0.5 mm x 6.0 mm during penetrating keratoplasty induces 4 to 7 diopters of corneal astigmatism, with the steeper meridian along the axis of tissue deficiency. Corneal topography and vector analysis of astigmatism showed steepening along the axis of tissue deficiency and flattening 90 degrees away.