Objective To analyze corneal tomography and anterior and posterior corneal topography by Zernike polynomial fitting in the diagnosis of keratoconus. Methods Keratoconus patients (n=20, 30 eyes) and normal subjects (n=30, 30 eyes) were recruited for this case-controlled study. The Pentacam system was used to gather pachymetry data of the entire cornea and the elevations of the anterior and posterior corneal surfaces. Zernike polynomial fitting was used to quantify the 3D distribution of the corneal anterior and posterior surface elevations and thickness to obtain the root mean square (RMS) values for 2nd to 7th order and the higher-order aberration (HOA). Statistical analysis methods included independent samples t-test and receiver operating characteristic (ROC) curves. Results The 2nd to 7th order and the HOA RMSs of the anterior and posterior surface elevation and pachymetry were significantly different in the keratoconus patients compared to the normal subjects (P＜0.001). Among the corneal anterior surface elevation and pachymetry parameters, the 3rd, 5th, and HOA RMSs had high diagnostic accuracy. The areas under the ROC curves for anterior surface elevation were 0.999, 0.982, 0.994, and for pachymetry they were 0.993, 0.989, 0.992. The 3rd, 5th, 7th, and HOA higher-order RMSs of the corneal posterior surface elevation also had high diagnostic accuracy. The areas under the ROC curves were 0.997, 0.991, 0.993, 0.981. Among these parameters, the 3rd RMS for the corneal posterior surface elevation had the highest diagnostic accuracy with an area under the ROC curve of almost 1.000. Conclusion Based on Pentacam images to assess the characteristics of the entire corneal topography and tomography, the Zernike polynomial application, especially the 3rd RMS values, had good accuracy in the diagnosis of keratoconus.