Influence of the central corneal zone of patients on the measurement of keratometric parameters and the resultant KISA% index classification

Purpose: To analyze the influence of certain diameters of the corneal zone of a selected group of patients on the measured values of keratometric parameters and the resultant KISA% index classification.Methods: One hundred and two eyes from fifty-one volunteers born in the central region of Mexico, between 25 and 40 years old, without previous diagnosis or treatment for keratoconus, were enrolled in this retrospective study.The same ophthalmologist evaluated all patients, and the same technician measured their keratometric parameters using the same topographer, an Orbscan II Topography System.The influence of the corneal zone on the resultant KISA% index was analyzed using the formalism of the Receiver Operating Characteristic (ROC) curves.Results: As a consequence that the Area Under the ROC Curve (AUC) obtained with data for a 5.0 mm corneal zone diameter is larger than the AUC obtained for a 3.0 mm corneal zone, the ability to discern between normal and suspected eyes increased by 11%; between suspected eyes and those confirmed with keratoconus increased by 1.2%; and between normal eyes and those confirmed with keratoconus increased by 1.1%. Conclusion:From the analysis of the resultant ROC curves and the AUC, we demonstrated that, for a 5.0 mm corneal zone, the KISA% index results in a more reliable diagnostic.The discrimination between normal and suspected eyes can be difficult under certain circumstances; however, we achieved a more accurate diagnostic for discriminating normal eyes from suspected eyes when a 5.0 mm corneal zone is used instead of a 3.0 mm corneal zone.