Evaluation of corneal elevation in eyes with subclinical keratoconus and keratoconus using Galilei double Scheimpflug analyzer

PURPOSE. To measure corneal elevations in eyes with subclinical keratoconus and those with keratoconus using the Galilei Scheimpflug analyzer and to determine the optimal corneal elevation cutoff points to maximize sensitivity and specificity in discriminating keratoconus and subclinical keratoconus from normal corneas. METHODS. A total of 136 normal eyes, 23 eyes with subclinical keratoconus, and 51 eyes with keratoconus were enrolled. Maximum anterior and posterior corneal elevation was measured in the central 3-, 5-, and 7-mm zones using the Galilei double Scheimpflug camera. Receiver operating characteristic curves were used to compare the sensitivity and specificity of the measured parameters and to identify optimal cutoff points for discriminating keratoconus and subclinical keratoconus from normal corneas. RESULTS. Mean anterior and posterior corneal elevations in all zones were statistically higher in keratoconus and subclinical keratoconus versus normal corneas. The posterior elevation measurement in the 3-mm zone had the strongest power to distinguish keratoconus from normal. The corresponding figure for the 7-mm zone, however, had the strongest power to distinguish eyes with subclinical keratoconus (area under the curve, 0.98 and 0.92, respectively). Optimal cutoff point for posterior elevation in the 3-mm zone was 18.5 pm for keratoconus (sensitivity, 92%; specificity, 95%). The corresponding figure in the 7-mm zone was 50.5 mu m for subclinical keratoconus (sensitivity, 79.9%; specificity, 94.0%). CONCLUSIONS. Anterior and posterior elevations measured by the Galilei analyzer in the 3-mm zone can effectively discriminate keratoconus from normal corneas. These measurements in the 7-mm zone can be considered to distinguish subclinical keratoconus.