We developed the corneal asphericity index (CAI), which indicates the asphericity of the central cornea using the TMS-1 videokeratoscope, and used the CAI to evaluate both normal corneas and corneas with rigid gas permeable (RGP) lens induced warpage. The CAI (mean +/- standard deviation) for the 22 control corneas was 0.33 +/- 0.26, which indicates that the normal central cornea has a prolate shape. The average CAI for the 24 corneas with RGP lens induced warpage was significantly lower (-0.15 +/- 0.36, P = 0.0001). These data suggest that some corneas have abnormal asphericity in the central cornea when warpage occurs with RGP lenses. CAI is useful for the quantitative assessment of asphericity and topographic abnormalities in the central cornea caused by contact lens induced warpage.