Comparison of Corneal Reconstruction Between Casia 2 and Pentacam

Abstract

Purpose : The objective of this research is to comprehensively compare the anterior and posterior corneal surface reconstruction capabilities of Casia 2 and Pentacam, exploring their imaging principles, capabilities, and clinical utility. Through this analysis, we aim to highlight each modality's distinct advantages and provide insights into their complementary roles in enhancing ophthalmic modelling capabilities.

Methods : This study includes 50 right eyes from 50 adults (40 females and 10 males), with a mean age of 35 ± 8 years. The evaluation involved six measurements in two separate sessions using both CASIA 2 (Tomey, Nagoya, Japan) in corneal mode and Pentacam (Optikgeräte, Wetzlar, Germany), based on anterior segment OCT and Scheimpflug corneal tomography, respectively. Elevation maps were fitted to an 8 mm circular zone using a biconic surface. To prevent potential misalignment discrepancies, a Zernike polynomial surface of order six was initially fitted, extracting symmetric and astigmatic terms. From the geometric parameters (R_x,R_y,Q_x,Q_y) repeatability (R coefficient, 1.96√2σ) and reliability within and between devices (ICC coefficient, "Two-way mixed effects", absolute agreement) were calculated using Matlab 2023a. In addition, astigmatism was determined from the wavefront of anterior and posterior corneal elevation maps with Zemax.

Results : The table below shows R, variability within a single session, ICC_C,P, variability between two sessions, and ICC_C-P, variability between both devices in one session. Being the initial two displayed as a ratio to illustrate the extent of variation between devices.

Table 1

Finally, the estimated astigmatism for Casia 2 and Pentacam was -0.45 [0.53] and -0.41 [0.59] D, respectively. Non-statistically significant differences were observed (“Wilcoxon signed rank test”, p = 0.49).

Conclusions : Regarding the anterior surface, Casia 2 exhibits higher inter-subject variability than Pentacam; the opposite is true for the posterior surface. Despite this, intra-session variability is similar on both surfaces. When analyzing reliability between the devices of the anterior surface, the correspondence is close to unity, unlike the posterior one. Nevertheless, no significant differences in corneal astigmatism were found between the two devices.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Table 1. R, ICC_C,P and ICC_C-P across both devices of (R_x,R_y,Q_x,Q_y) for both corneal surfaces are shown.