Comparison of anterior corneal aberrometry, keratometry and pupil size with Scheimpflug tomography and ray tracing aberrometer in moderate and high refractive error

Abstract

Background: Keratometry is essential for assessing corneal curvature, refractive power, and astigmatism. Advances in imaging, such as topography and tomography, have improved measurement accuracy for surgical planning and disease diagnosis. The Pentacam HR® uses Scheimpflug imaging for higher-order aberrations (HOAs), while iTrace® employs ray tracing for wavefront aberrometry.

Aim: This study compared anterior corneal wavefront aberrations, keratometry, astigmatism axis, and pupil size measurements between Pentacam HR® and iTrace® in moderate and high refractive error.

Methodology: A retrospective observational study at a tertiary care hospital in north India analysed 202 eyes from 107 healthy volunteers under mesopic conditions. Parameters included spherical aberration (Z40), vertical coma (Z3−1), horizontal coma (Z3+1), trefoil (Z3−3, Z3+3), keratometry (K1, K2), and pupil size.

Results: The mean age was 26.73 ± 5.05 years. Significant differences were noted in keratometry: Pentacam HR® recorded higher K Flat (43.78 ± 1.70 D vs. 41.38 ± 3.64 D, p < 0.001) and K Steep (45.09 ± 1.84 D vs. 43.19 ± 3.49 D, p < 0.001). K Flat Axis differed (p = 0.013), while K Steep Axis did not (p = 0.419). Pupil size was larger with iTrace® (5.71 ± 0.91 mm vs. 2.90 ± 0.62 mm, p < 0.001). Coma (Z3−1), trefoil (Z3−3), and trefoil (Z3+3) showed significant differences (p < 0.001), while spherical aberration (Z40) (p = 0.828) and horizontal coma (Z3+1) (p = 0.200) did not. Bland-Altman plots showed poor agreement for axis measurements, moderate for keratometry, and better for HOAs.

Conclusion: Significant differences in keratometry, pupil size, and HOAs indicate that Pentacam HR® and iTrace® measurements are not interchangeable. Clinicians should consider these discrepancies, especially in high refractive error cases.