Inter-device Agreement of Device-Designated Chord Mu and Chord Alpha Measurements in Patients Undergoing Preoperative Cataract Evaluation.

Abstract

Purpose: To evaluate inter-device agreement of device-designated chord mu and chord alpha measurements, defined as device-designated linear displacements between the Purkinje reflex and the pupil center (chord mu) or limbal center (chord alpha), by four common devices: IOLMaster 700 (Carl Zeiss Meditec AG), Lenstar 900 (Haag-Streit), iTrace (Tracey Technologies), and Pentacam (Oculus Optikgeräte GmbH).

Methods: This was a retrospective cross-sectional study of patients undergoing preoperative cataract evaluation at a tertiary academic center. Eyes with measurements from all four devices between 2020 and 2023 were included. Exclusion criteria included prior ocular trauma, surgery, or pathology affecting imaging. Chord mu and alpha were analyzed using bivariate methods, including centroid direction and inter-device comparisons. Biometry and corneal curvature were also analyzed.

Results: A total of 110 eyes from 77 patients (mean age: 63 ± 11 years) were included. Across devices, mean chord mu values were approximately 0.35 ± 0.20 mm and mean chord alpha values were approximately 0.45 ± 0.23 mm, with substantial variability in both magnitude and orientation. Most pairwise inter-device comparisons demonstrated statistically significant differences for both chord mu and chord alpha. The IOLMaster 700 consistently demonstrated temporal centroid displacement and the widest directional dispersion, whereas other devices showed predominantly nasal centroid orientation. Left and right eyes demonstrated similar patterns but were analyzed separately.

Conclusions: Clinically relevant inter-device differences in magnitude and orientation of chord mu and chord alpha were observed, with systematic centroid shifts and directional dispersion. These device-specific offsets indicate that such measurements are not interchangeable across platforms and should be interpreted in the context of the measuring device when applied to surgical planning.