effect of relaxing incisions for post penetrating keratoplasty astigmatism on graft curvature

purpose: to evaluate changes in graft steepness after graft refractive surgery (grs) and to discover influential factors and a coefficient to predict the amount of postoperative shift. methods: keratoconic patients with history of penetrating keratoplasty (pkp) who underwent grs due to high post-pkp astigmatism were included. changes in mean keratometry after grs were evaluated to find possible influential factors such as age, graft anatomical features, number of incisions, use of compression sutures, and total arc length on achieved vector astigmatic correction. results: there was a significant increase in average keratometry by 0.86±1.07 d postoperatively (p<0.001). mean keratometric coupling ratio (cr) and coupling constant (cc) were 0.62±1.09 and -0.34±0.70, respectively. a significant association was found between preoperative spherical equivalent keratometry and keratometric cr, and between achieved correction in vector keratometric astigmatism and keratometric cc. additionally, age had a significant negative association with keratometric cr and cc. conclusion: a significant increase in graft steepening occurred after grs. for every diopter reduction in vector keratometric astigmatism, a mean of 0.34 d increase in graft curvature is expected postoperatively.