Factors affecting changes in astigmatism before and after suture removal following penetrating keratoplasty.

PURPOSE To analyze the factors related to changes in astigmatism before and after suture removal in patients who underwent penetrating keratoplasty (PK). METHODS The study group consisted of 171 consecutive PKs in 171 patients. Keratometric astigmatism was measured before and after suture removal in all patients. The vectorial difference for each eye was calculated between the examination before suture removal and the first year after suture removal. The vectorial difference values were compared with the possible factors affecting astigmatic change such as age of the patient, donor-recipient trephine diameter difference, preoperative diagnosis, and time of suture removal. All sutures were removed completely in one session. The vectorial difference values of all groups were compared with each other statistically. RESULTS Before suture removal, the mean cylinder was 4.40 +/- 3.24 D; it was 3.96 +/- 2.19 D at 1 year after suture removal. The net difference of astigmatism was -0.27 +/- 3.50. The mean value of vectorial difference for all patients was 4.93 +/- 4.02 D. There was a statistically significant negative correlation between the trephine diameter difference and the vectorial difference (r= -0.582, p<0.01). There was a significant change in vectorial difference values in patients with high pre-suture removal astigmatism. Patients with keratoconus had a positive correlation between the pre-suture removal astigmatism and the vectorial difference (r=0.615, p=0.038). CONCLUSIONS After suture removal following PK, unexpected high levels of astigmatic change could be encountered due to donor-recipient trephine diameter difference and underlying primary diagnosis such as keratoconus. In particular, high level astigmatism before suture removal has a greater risk of increased astigmatic change after suture removal.