Comprehensive anterior segment normal values generated by rotating Scheimpflug tomography.

PURPOSE: To identify normal values for tomographic parameters that are considered useful in screening patients for refractive surgery.

SETTING

Private center, Albany, New York, USA.

DESIGN

Database study.

METHODS

A Pentacam HR Scheimpflug system was used to examine 1 randomly selected eye of patients to determine normal values of 21 parameters considered the most clinically applicable for surgical screening. Normality of data was evaluated using the Kolmogorov-Smirnov test. Statistical analyses were performed using the Student t test to compare means and the 2-paired sample Wilcoxon signed-rank test. Results are displayed in 95.0% and 97.5% confidence intervals (CIs).

RESULTS

The study evaluated 341 adults. High-end outliers at the 97.5% CI were 46.1 diopters (D) for flat keratometry (K), 47.4 D for steep K, 3.4 D for astigmatism, 3.8 μm for anterior chamber depth, 4 μm for front apical elevation, 5 μm for front elevation at the thinnest point, and 12 μm for front elevation in the central 4.0 mm. Respective posterior elevation values were 7 μm, 13 μm, and 25 μm, with a progression index maximum of 1.53 and mean of 1.19, difference between apical and thinnest pachymetric reading of 7 μm, a maximum K of 48.2 D, and an inferior-superior ratio of 1.44 D. Low-end outliers were a maximum Ambrósio relational thickness of 335 and a mean of 425, minimum pachymetry of 479 μm, thickness at the apex of 481 μm, and central 4.0 mm corneal volume of 6.31 mm(3).

CONCLUSION

Scheimpflug-derived corneal tomography identified key refractive surgery parameters that may be useful in screening refractive surgical patients.