KISA% index: A quantitative videokeratography algorithm embodying minimal topographic criteria for diagnosing keratoconus

Purpose: To formulate and test an algorithm using minimal topographic crite ria for accurately diagnosing clinical keratoconus. Setting: Subspecialty cornea practice and Keratoconus Genetic Research Proj ect. Methods: Both eyes of 86 keratoconic patients who had never worn contact le nses and 195 normal participants were studied with the TMS-1 videokeratosco pe to evaluate the KISA% index, an algorithm that topographically quantifie s the phenotypic features of keratoconus. The diagnostic efficacy of the KI SA% index was compared with that of the modified Rabinowitz/McDonnell (K- a nd I-S values) and the Maeda/Klyce (KCl% and KPl) indices. The same indices were calculated for an additional 8 eyes with keratoconus-suspect topograp hy and 12 eyes with early keratoconus. Results: The mean KISA% was significantly greater in the keratoconus group (10 382%) than in the normal control group (20.44%) with minimal overlap. A t a cutoff point for KISA% of 100, 280 of 281 participants (99.6%) were cor rectly classified, in contrast, the correct classification rate for the oth er indices were KCl%, 274 of 281 (97.5%); KPl, 249 of 281 (88.6%); K, 272 o f 281 (96.8%); I-S, 269 of 281 (95.7%). Six of the 8 eyes with keratoconus- suspect topography had a KISA% between 60% and 100%, and 11 of the 12 eyes with early keratoconus had a KISA% greater than 100%. Conclusions: The KISA% index set at 100 was highly sensitive and specific f or diagnosing keratoconus; a range of 60% to 100% may be useful for designa ting suspects. this index is more useful than any of the other currently av ailable tools for classifying patients with keratoconus for computerized se gregation analysis and for distinguishing eyes with keratoconus from normal eyes in topographic screening of refractive surgical candidates. (C) 1999 ASCRS and ESCRS.