Posterior corneal shape: a comparison of height data from three corneal topographers

Document Type



Available under a Creative Commons Attribution Non-Commercial Share Alike 4.0 International Licence


Optics, Other biological topics, Anatomy and morphology, Ophthalmology

Publication Details

Journal of Cataract & Refractive Surgery , Vol. 43 , Issue 4 , 518 - 524



Purpose: To compare three clinical corneal topographers in their ability to describe the posterior corneal shape.

Methods: The corneas of 30 eyes of 30 healthy subjects were measured twice with a dual Scheimpflug camera (Galilei), a scanning slit system (Orbscan), and a single Scheimpflug camera (Pentacam). Elevation data describing the posterior corneal shape were fitted with Zernike polynomials. Mean values with standard deviation (SD), test-retest variability (coefficient of repeatability), and inter-device variability were determined for the defocus (z[2,0]), astigmatism (z[2,-2], z[2,2]), coma (z[3,-1], z[3,1]), trefoil (z[3,-3], z[3,3]), and spherical aberration (z[4,0]) coefficients, for 5.5 and 8.0 mm diameter zones.

Results: At 5.5 mm, the mean (SD) Zernike coefficients were, for the Galilei, +176 (7), +0.1 (1.3), -6.6 (2.4), +0.3 (0.8), +0.1 (0.8), -0.4 (0.5), +0.9 (0.6), and 1.6 (0.6) for z[2,0], z[2,-2], z[2,2], z[3,-1], z[3,1], z[3,-3], z[3,3], and z[4,0], respectively. The coefficients of repeatability ranged from 0.3 to 4.3 μm for the Galilei, from 1.6 to 5.2 for the Orbscan, and from 0.3 to 2.0 μm for the Pentacam; the repeatability was similar for Galilei and Pentacam (p=0.43) and significantly poorer for the Orbsan (p

Conclusions: For the assessment of the posterior corneal shape, the repeatability is generally good for the Galilei and Pentacam but poor for the Orbscan. Interdevice variability between Galilei and Pentacam compromises the exchangeability of the devices’ measurement values.