Revisiting corneal topography for the diagnosis of keratoconus: use of Rabinowitz's KISA% index

Background: Numerous videokeratographic methods are used in the diagnosis of keratoconus. The purpose of this study was to compare the sensitivity and specificity of the KISA% index with the keratometry (K) value, inferior-superior (I-S) value, relative skewing of the steepest radial axes (SRAX), and keratometric astigmatism (AST) indices in 25 patients presenting with bilateral keratoconus. Methods: Twenty-five patients presenting with bilateral keratoconus were enrolled. Fifty eyes from 25 healthy individuals without corneal abnormalities were used as controls. The clinical diagnosis of keratoconus was made by observation of scissors reflex at retinoscopy and characteristic slit lamp findings. Corneal topographic analysis was performed in each eye to calculate the K value, I-S value, AST, and SRAX indices. Results: The keratoconus percentage index (KISA%) was significantly more sensitive and specific than the other indices examined. Furthermore, it was significantly better at predicting positive and negative results than the other indices included in the study. Conclusion: The current research suggests that KISA% could be used to detect/diagnose keratoconus but further studies are required to confirm the specificity and sensitivity of KISA% for the detection of early-stage disease and keratoconus suspects.