Comprehensive Evaluation of Anterior Corneal Change in Asphericity Calculated by the Tangential Radius of Curvature after LASIK

Abstract

To evaluate the change in the anterior corneal asphericity (ΔQ) comprehensively calculated using the tangential radius (rt) after LASIK. Forty-two right eyes were evaluated using the Orbscan II corneal topographer. The pre- and postoperativeQ-values of the flat principal semimeridians calculated by the sagittal radius were compared to those by the tangential radius. TheQ-value of each semimeridian in the horizontal region was calculated byrt. Fourier fitting was used to model the 360-semimeridional variation ofQ-values and to fit theQ-values in the vertical region before and after surgery. There were significant differences inQ-values between the two methods before (P<0.001) and after surgery (P=0.003). A significant increase in postoperativeQ-value was detected compared to preoperativeQ-value (P<0.001) calculated byrt. The 360-semimeridional variation of theQ-values was well fitted with a third- and fourth-degree Fourier function before and after surgery. The ΔQ-value distribution presented double valley variation, with the amount of ΔQbeing lowest in the near-vertical regions and highest in the near-horizontal regions. Calculating theQ-value withrtcombined with Fourier fitting, we evaluated 360 ΔQ-values’ variation of semimeridians of the entire anterior corneal surface and then displayed true and complete anterior corneal shape after LASIK.