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Repeatability and agreement between a reference Scheimpflug tomographer and a low-cost Scheimpflug system
Wenjun Xu1, Changbin Zhai, Mayinuer Yusufu
1From the Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology & Visual Science Key Lab, Beijing, China (Xu, Zhai, Gan, Li, Zheng, Kang); Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, East Melbourne, Australia (Yusufu); Department of Surgery (Ophthalmology), The University of Melbourne, Melbourne, Australia (Yusufu).
Purpose:
To assess the repeatability and agreement between Scheimpflug-based corneal topographers, Scansys and Pentacam, in measuring ocular parameters in myopic eyes.
Setting:
Grade-A tertiary hospital in Beijing, China.
Design:
Cross-sectional study.
Methods:
The following measurements were performed in 204 subjects undergoing preoperative examinations for refractive surgery from the corneal curvature, astigmatism, corneal thickness, corneal volume, corneal asphericity, anterior chamber depth (ACD) and volume (ACV), and pupil diameters. Repeatability was determined using intraclass correlation coefficient with 95% CI, Cronbach α, coefficient of variation, within-subject SD, test-retest repeatability, and 1-way analysis of variance (1-way analysis of variance). The interdevice agreement was determined using paired t test and Bland-Altman plots.
Results:
Scansys showed good repeatability in the anterior and posterior corneal flattest meridian (Kf), steepest meridian (Ks), and mean (Km); axis of anterior corneal Ks; anterior corneal astigmatism; pupil central corneal thickness (CCT); CCT; corneal apex thickness; thinnest corneal thickness; corneal volume; photopic pupil diameter; ACD; and ACV. In the agreement study, Bland-Altman plots showed that 95% limit of agreement of corneal curvature, pupil CCT, corneal apex thickness, thinnest corneal thickness, and corneal volume generated by Scansys and Pentacam were narrow. There were no statistically significant differences in the anterior corneal Kf and Km.
Conclusions:
Scansys showed good repeatability in measuring corneal curvature of anterior and posterior surfaces, anterior corneal astigmatism, corneal thickness, corneal volume, photopic pupil diameter, ACV, and ACD. Scansys and Pentacam can only be used interchangeably in measuring anterior corneal curvature.
