At least 10% of penetrating keratoplasty patients have postoperative astigmatism precluding useful vision. A substantial contributor to this astigmatism is misalignment of oval donor buttons in oval recipient beds, such that exiguous tissue produces steep curvature and excess tissue flat curvature. This research proposes to determine the influence of the button and bed fit on the direction, amount, and asymmetric character of corneal astigmatism as measured by photogrammetry after penetrating keratoplasty in adult cats. Peroperative tissue alignment will be compared with postoperative corneal topography in our feline laboratory model for penetrating keratoplasty. The recipient beds of the right eyes of 40 cats and the donor buttons from both eyes of 20 cats will be ovally trephined from intact globes. Buttons will be positioned in beds to produce a full range of alignments. Photographs of the endothelial edges of recipient and donor buttons will be enlarged and traced. By the Fit Assessment Method (FAM) the traced endothelial edges will be digitized and overlayed in corresponding pairs to determine the meridians of maximum tissue overlap, minimum tissue overlap or gap, and a predicted wound margin. The ring reflections of postoperative keratographs taken over nine postoperative months, the predicted endothelial wound margin, and the healed endothelial wound margin as recorded by scanning electron photomicrographs will be processed by our Photogrammetric Index Method (PIM). PIM identifies major and minor meridians of closed loops which correspond to the corneal meridians of flattest and steepest curvature respectively. PIM also indexes the closed loops' departure from circularity. The directions of peroperative meridians of greatest and least tissue will be compared with the directions of postoperative meridians of flattest and steepest corneal curvature. The asymmetric character of the predicted and healed wound margins will be compared with the astigmatic character of the postoperative keratographic rings. Differences between amounts of tissue along the maximum and minimum tissue fit meridians will be compared with the amount of postoperative astigmatism. Total tissue overlap will be compared with mean postoperative keratometry. These relationships will be correlated with healing course indicators, and their significance will be assessed by correlation regression analyses and non-parametric methods. Thus peroperative variables relevant to postoperative astigmatism will be identified.
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