Repeatability and Agreement of Chord Mu between Scheimpflug Tomography and Swept-Source Optical Coherence Tomography

Abstract

Purpose: To evaluate repeatability and agreement of chord mu between Scheimpflug tomography (Pentacam HR) and sweptsource optical coherence tomography-based optical biometer (IOLMaster 700).

Methods: In this retrospective study, 63 eyes from 33 patients were included. Chord mu, X and Y Cartesian distances between the corneal vertex and the pupil center (Px and Py), and the pupil diameter were compared using two instruments. Repeatability was evaluated using intraclass correlation coefficient (ICC), coefficient of variation (CoV), and within-subject standard deviation (Sw). Interdevice agreement was evaluated using paired t-tests and Bland-Altman plots.

Results: Although Sw values for all parameters were similar between the two devices, CoV values of chord mu and pupil diameter were lower, and ICC values of those parameters were higher, in the IOLMaster 700 than in the Pentacam HR. Chord mu and pupil diameter values were higher in IOLMaster 700 than Pentacam HR (p < 0.01). The width of the 95% limit of agreement was wide for all parameters.

Conclusions: IOLMaster 700 showed better repeatability than Pentacam HR in chord mu, Px, Py, and pupil diameter values. Because there were statistically significant differences and a low level of agreement in chord mu and pupil diameter values between the two devices, they cannot be used interchangeably.

Keywords: Angle kappa; Chord mu; Pupil diameter; Scheimpflug tomography; Swept-source optical coherence tomography.

Fig. 1

Graphic demonstrations of ocular reference axes, angles, and chord mu. (A) Angle kappa represents the angle between pupillary axis and visual axis and angle lambda represents the angle between pupillary axis and line of sight. (B) Chord mu is the distance between corneal vertex and pupil center. Px = X Cartesian distance between corneal vertex and pupil center; Py = Y Cartesian distance between corneal vertex and pupil center.

Fig. 2

Representative outcome images of pupil diameter, chord mu and X and Y Cartesian distance between corneal vertex and pupil center in (A) Pentacam HR (Oculus) and (B) IOLMaster 700 (Carl Zeiss Meditec Inc). CCT = central corneal thickness; WTW = white-to-white; Px = X Cartesian distance between corneal vertex and pupil center; Py = Y Cartesian distance between corneal vertex and pupil center.

Fig. 3

The Bland-Altman plots of ocular parameters agreement between IOLMaster 700 (Carl Zeiss Meditec Inc) and Pentacam HR (Oculus). (A) Chord mu. (B) Pupil diameter. (C) X Cartesian distance between corneal vertex and pupil center (Px). (D) Y Cartesian distance between corneal vertex and pupil center (Py). SD = standard deviation.