Effect of penetrating keratoplasty using grafts of various sizes on keratoconic myopia and astigmatism.

The records of 72 consecutive keratoconic eyes undergoing penetrating keratoplasty were reviewed for changes in myopia and astigmatism. Ages of the patients averaged 32.7 years. All sutures were removed after three months. Follow-up average was 40.2 months. Results showed an average decrease in myopia of 6.63 diopters (D) in 60 eyes (82.86%) and an average increase in myopia of 1.88 D in 12 of 70 eyes (17.14%). The decrease/increase in myopia and postoperative astigmatism was compared for grafts equal to the opening, grafts smaller than the opening, and grafts larger than the opening. The largest average decrease in myopia was 13.86 D (range 6.63 to 20.00), which occurred when a graft smaller than the opening was used (P less than .01). This group also showed the least postoperative astigmatism (2.82 D) (P less than or equal to .01). From this study, it appears that the use of a graft 0.25 mm smaller than the trephine opening in the host (i.e., 7.50 mm graft/7.75 mm opening) for penetrating keratoplasty in keratoconus is justified. A prospective study is now in progress.