Multivariate model of refractive shift in Descemet-stripping automated endothelial keratoplasty

PURPOSE:To relate in situ graft shape in Descemet-stripping automated endothelial keratoplasty (DSAEK) to surgically induced refractive error. SETTING:Academic eye institute. METHODS:High frequency arc-scanning ultrasound was performed in 7 patients enrolled in a prospective study of microkeratome-assisted endothelial keratoplasty approved by the Investigative Review Board. A region of interest spanning the horizontal meridian was defined for analysis of epithelial, host, graft, and total corneal thicknesses. Graft thickness profiles were fit by quadratic polynomials where the 2nd-order coefficients represent the posterior corneal curvature contributed by the graft. The curvature coefficient and central graft thickness were analyzed as predictors of induced refractive error. RESULTS:At final follow-up (mean 5.9 months +/- 3.2 [SD]), 3 patients had a hyperopic shift (+2.50 diopters [D] each), 3 had insignificant (< 0.50 D) refractive shifts, and 1 had a myopic shift. In the group with hyperopic shift, a negative lens effect was predicted by positive curvature coefficients, representing grafts that were thinner centrally than peripherally (mean +22.72 microm/mm(2); range +4.95 to +45.17 microm/mm(2)). In the group with minimal refractive shift, coefficients were less positive (mean +7.28 microm/mm(2); range +2.01 to +13.82 microm/mm(2)). The patient with a myopic shift (-1.00 D) had the only negative curvature coefficient (-0.64 microm/mm(2)). In a 2-predictor model of refractive shift, central graft thickness and the curvature coefficient together accounted for 86% of the variance in the refractive response to DSAEK (P = .025). CONCLUSION:Nonuniform thickness profiles and variable central graft thicknesses both contribute to refractive shift after DSAEK.