Comparative study of the corneal morphological characteristics of keratoconus evaluated using CASIA2, Sirius, and Pentacam

Abstract Purpose To analyze the corneal morphology of keratoconus using CASIA2, Sirius, and Pentacam. Methods Patients diagnosed with keratoconus at the Eye and ENT Hospital of Fudan University (January-November 2022) were included. Corneal refraction, astigmatism, thickness, and elevation parameters were measured using CASIA2, Sirius, and Pentacam. The measurement differences, agreement, and the sensitivity and specificity of each instrument for diagnosing keratoconus was evaluated. P < 0.05 was considered statistically significant. Results A total of 61 keratoconus eyes and 48 healthy myopic eyes were included. The Ks and Kf measured using Sirius were the highest (p < 0.0001). The thinnest corneal thickness measured using Pentacam was the thickest (p < 0.0001); however, the significance disappears in the Kmax ≤ 48D keratoconus group. When the best fit sphere was based on CASIA2, the anterior and posterior elevations at thinnest points measured using Sirius were the highest in keratoconus group and the lowest in control group. Corneal refractive power measurements significantly differed among instruments (p < 0.0001). In the control group, the agreement limits for total corneal refractive power (TCRP), fKm, and pKm were lower and narrower than in keratoconus. In keratoconus group, Pentacam and CASIA2 showed the best consistency in the measurement of TCRP and fKm, whereas Pentacam and Sirius showed the best consistency in the measurement of pKm. Sensitivities for diagnosing keratoconus ranked from high to low: Pentacam, CASIA2, Sirius (p < 0.0001). Conclusion CASIA2, Sirius, and Pentacam exhibit differences in corneal elevation, refractive power, and thickness measurements, with poor consistency in refractive power measurement.