Central and peripheral corneal thickness measurement in normal and keratoconic eyes using three corneal pachymeters

Abstract

Purpose: To assess the agreement among ultrasonic pachymetry, the Galilei dual Scheimpflug analyzer, and Orbscan II for central and peripheral (Galilei vs. Orbscan) corneal thickness (CCT and PCT) measurement in normal and keratoconic eyes.

Methods: In this prospective study, CCT and PCT were measured in 88 eyes of 88 refractive surgery candidates and 128 eyes of 69 keratoconic patients with ultrasonic pachymetry, the Galilei, and Orbscan II. The readings by the three instruments were compared using one-way analysis of normal variance. Agreement among the three devices was assessed using Pearson and intraclass correlation coefficients, and Bland-Altman plots. The same analyses were employed to evaluate agreement between Galilei and Orbscan II for PCT measurement.

Results: In the normal group, mean CCT was 551.0±39.4, 566.9±33.5, and 565.5±40.9 μm measured by ultrasonic pachymetry, the Galilei, and Orbscan II, respectively (P<0.001). The corresponding figures in the keratoconus group were 492.0±61.7, 502.0±42.1, and 470.6±56.9 μm, respectively (P<0.001). Mean PCT was 612.5±35.3 and 640.9±38.0 μm in the normal group (P<0.001) and 567.6±35.2 and 595.1±41.4 μm in the keratoconus group (P<0.001) by the Galilei and Orbscan II, respectively. CCT and PCT measurements obtained by different devices were significantly correlated in both groups.

Conclusion: To measure CCT, the Galilei and Orbscan II can be used interchangeably in normal eyes, but not in keratoconic eyes. For PCT, there is a systematic error between measurements obtained by the Galilei and Orbscan II. However, it is possible to change optical pachymeter readings into those obtained by ultrasonic pachymetry using a constant.

Keywords: Central Corneal Thickness; Galilei; Keratoconus; Orbscan II; Peripheral Corneal Thickness; Ultrasonic Pachymetry.

Figure 1

Scatter plot of central corneal thickness in the normal group measured with ultrasonic pachymetry against the Orbscan II system (a), ultrasonic pachymetry against the Galilei system (b), and Orbscan II against the Galilei system (c). The solid lines represent the fit and the dotted lines represent the 45° angle.

Figure 2

Scatter plot of central corneal thickness in the keratoconus group measured with ultrasonic pachymetry against the Orbscan II system (a), ultrasonic pachymetry against the Galilei system (b), and Orbscan II against the Galilei system (c). The solid lines represent the fit and the dotted lines represent the 45° angle.

Figure 3

Scatter plot of peripheral corneal thickness in the normal (a) and keratoconus (b) groups measured with the Galilei system against the Orbscan II system.

Figure 4

Bland–Altman plots in the normal group; difference of central corneal thickness against mean central corneal thickness measured with the Orbscan II system and ultrasonic pachymetry (a), with the Galilei system and ultrasonic pachymetry (b), and with the Galilei and Orbscan II systems (c). The solid (middle) lines indicate the mean difference and the dotted (side) lines represent the upper and lower borders of the 95% limits of agreement.

Figure 5

Bland–Altman plots in the keratoconus group; difference of central corneal thickness against mean central corneal thickness measured with the Orbscan system and ultrasonic pachymetry (a), with the Galilei system and ultrasonic pachymetry (b), and with the Galilei and Orbscan II systems (c). The solid (middle) lines indicate the mean difference and the dotted (side) lines represent the upper and lower borders of the 95% limits of agreement.

Figure 6

Bland–Altman plots in the normal (a) and keratoconus (b) groups; difference of peripheral corneal thickness against mean peripheral corneal thickness measured with the Orbscan II and the Galilei systems.