Effect of Different Corneal Curvature on Corrected Power of Conductive Keratoplasty

Introduction conductive Keratoplasty (CK) induce refractive change of cornea by peripheral deformation. The predictability of CK is still unsatisfactory, partly due to wound-healing response and refractive regression. Because the same surgery operation was performed on corneas of different curvature, we infer that different curvature of cornea may be one of the reasons for diverse surgery results. In this paper, the effect of different curvature of cornea on corrected power of conductive keratoplasty was evaluated. Mathematical analysis was done on the assumption that front surface of deformation zone of cornea is spherical before and after surgery, back surface of cornea is stable before and after surgery. After surgical deformation, relative change of refractive power of front surface of cornea Delta Phi / Phi =(R-r)/r=-Delta R/h, where R is curvature radius of front surface of cornea before surgery, r is that after surgery, Delta R is the deformation of cornea at location of surgical operation, h is the difference of height between apex of cornea and location of surgical operation. Absolute change of refractive power of cornea Delta Phi ap -2(n-1)Delta R/L², where n is refractive index of cornea, L is the distance from the location of surgical operation to the axis of cornea. Calculation by the above formula with operation values of actual surgery shows that the absolute theoretical errors will be less than 0.1 diopter. Thus, refractive power change of cornea induced by peripheral deformation has linearity relationship with deformation and change rapidly with surgery location, but it is almost stable with different curvature of cornea. Both deformation and surgery location are parameters related to surgery response, surgery regression and surgery operation. Hence, different surgery response, surgery regression and unsatisfactory precision of surgery operation are main causes for unsatisfactory predictability of such surgery. New work to be presented Th- eoretical analysis shows that different curvature of cornea has little effect on corrected power of conductive keratoplasty.