effect of graft-recipient disparity on refractive outcomes in keratoconus

purpose: to compare the refractive results of penetrating keratoplasty (pk) in two groups of patients with keratoconus undergoing corneal grafting with different amounts of donor-recipient disparity (0.25 and 0.5 mm). methods: as a randomized clinical trial and after performing a complete ocular examination and vitreous length measurement, 30 patients with keratoconus were randomly assigned in two groups: 15 patients underwent pk with 0.25 mm graft-recipient disparity and the other 15 patients underwent the operation with 0.5 mm disparity. one surgeon performed all the operations using a single running suture technique. best corrected visual acuity and refractive errors were evaluated 1 year after pk and also two months after suture removal. results: one year after pk and also 2 months after suture removal there was no statistically significant difference in bcva between the two groups. mean spherical and mean spherical equivalent refractive error was better in the 0.25 mm group, however this difference was not statistically significant (p> 0.05). in vitreous length range of 16.2-17.7 mm (20 patients) mean spherical equivalent refractive error was     -1.6 and -3.6 d in the 0.25 mm and 0.50 mm disparity groups, respectively (p= 0.03). mean spherical error was also better in the 0.25 mm group as compared with the 0.5 mm group (-0.8 versus -2.6 d, p= 0.05). mean astigmatic refractive error was minimally different between the two groups. conclusion: less donor-recipient disparity (0.25 mm vs 0.50 mm) seems to lead to better refractive outcomes in penetrating keratoplasty for eyes with keratoconus and vitreous length of 16.2-17.7 mm.