Corneoscleral Topography Measured with Fourier-based Profilometry and Scheimpflug Imaging

Abstract

SIGNIFICANCE 

Precise measurement of corneoscleral topography makes a valuable contribution to the understanding of anterior eye anatomy and supports the fitting process of contact lenses. Sagittal height data, determined by newer noninvasive techniques, are particularly useful for initial scleral lens selection.

PURPOSE 

The purpose of this study was to investigate the agreement and repeatability of Fourier-based profilometry and Scheimpflug imaging, in the measurement of sagittal height and toricity of the corneoscleral region.

METHODS 

Minimal (Min_sag), maximal (Max_sag) sagittal height, toricity (Max_sag − Min_sag), and the maximum possible measurement zone diameter of 38 subjects were compared using the Eye Surface Profiler (ESP; Eagle Eye, Houten, the Netherlands) and the corneoscleral profile module of the Pentacam (Oculus, Wetzlar, Germany) at two different sessions. Correlations between the instruments were analyzed using the Pearson coefficient. Differences between sessions and instruments were analyzed using Bland-Altman and paired t tests.

RESULTS 

For an equal chord length, the measurement with Pentacam was significantly greater for Min_sag (344 μm; 95% confidence interval [CI], 322 to 364 μm; P < .001) and significantly greater for Max_sag (280 μm; 95% CI, 256 to 305 μm; P < .001), but significantly smaller for toricity (−63 μm; 95% CI, −95 to −31 μm; P < .001). Maximum possible measurement zone diameter with ESP (16.4 ± 1.3 mm) was significantly greater than with Pentacam (14.8 ± 1.1 mm) (P < .001). Repeated measurements from session 1 and session 2 were not significantly different for Pentacam and ESP (P = .74 and P = .64, respectively). The 95% CIs around differences indicate good repeatability for Pentacam (mean difference, −0.9 μm; 95% CI, −6.7 to 4.8 μm) and ESP (4.6 μm; −22.4 to 31.6).

CONCLUSIONS 

Although both instruments deliver useful data especially for the fitting of scleral and soft contact lenses, the sagittal height and the toricity measurements cannot be considered as interchangeable.