A combination of topographic and pachymetric parameters in keratoconus diagnosis.

Objective: To evaluate the utility of topographic and pachymetric parameters of Scheimpflug system in keratoconus diagnosis.

Methods: This study included 183 eyes of 183 patients with keratoconus (keratoconus group) and 131 eyes of 131 age and sex-matched healthy subjects (control group). Mean keratometry (K, front), topographic astigmatism, pupil-center pachymetry, apical pachymetry, thinnest pachymetry (TP), corneal volume and maximum K (Kmax) were obtained from the Scheimpflug imaging system. A receiver operating characteristic (ROC) analysis was performed and area under the curve (AUC) was calculated to determine the diagnostic ability of each parameter in eyes with ≤ stage 3, ≤ stage 2 and stage 1 keratoconus based on the Amsler-Krumeich grading system.

Results: The Kmax and TP showed the highest individual performance (with sensitivity-specificity of 92.9-92.4% and 89.6-93.3%, respectively) in diagnosis of keratoconus. The AUCs and sensitivity-specificity values for the Kmax/TP and Kmax(2)/TP were calculated to improve the diagnostic performance. As expected, sensitivity-specificity values significantly increased by using Kmax/TP (97.3-94.7% at the level ≥0.08) and Kmax(2)/TP (99.5-95.7% at the level ≥4.1) in discrimination of keratoconic eyes from normals. Moreover, Kmax(2)/TP had very high sensitivity (>99%) and specificity (>94%) in diagnosis of stage 1 and stage 2 keratoconus.

Conclusions: Although Kmax and TP appear to have high diagnostic ability in keratoconus, the use of either single parameter in isolation might be unsatisfactory in differential diagnosis. Therefore, the Kmax(2)/TP ratio has been introduced, which reflects major characteristics of keratoconus and might be used as an important criterion in keratoconus diagnosis.