Shape of the anterior cornea: Comparison of height data from 4 corneal topographers

Abstract

To compare the ability of clinical corneal topographers to describe the shape of the anterior cornea for optical modeling. University Medical Center Groningen, Groningen, Netherlands. Cross-sectional study. The anterior corneal shape of healthy subjects was assessed with 4 topographers (AtlasPlacido disk, Galilei dual Scheimpflug, Orbscan scanning slit, Pentacam single Scheimpflug). Exported height data were fit with Zernike polynomials. Mean values with the standard deviation, interdevice variability, and test-retest variability were determined for the defocus Z(2,0), astigmatism Z(2,-2) and Z(2,2), coma Z(3,-1) and Z(3,1), and spherical aberration Z(4,0) coefficients for 5.5 mm and 8.0 mm diameters. At 5.5 mm, the single Scheimpflug topographer showed the smallest coefficient of repeatability; 0.31 μm for Z(2,0); 0.40 and 0.34 μm for Z(2,-2) and Z(2,2), respectively; 0.15 and 0.11 μm for Z(3,-1) and Z(3,1), respectively; and 0.08 μm for Z(4,0); the other topographers showed up to 10 times larger coefficients of repeatability. The (unsigned) mean differences between the topographers were in the range of 0.20 to 1.21 μm for Z(2,0); 0.02 to 0.31 μm and 0.06 to 0.42μm for Z(2,-2) and Z(2,2), respectively; 0.03 to 0.18 μm and 0.03 to 0.35 μm for Z(3,-1) and Z(3,1), respectively; and 0.00 to 0.14 μm for Z(4,0). The Placido-disk topographer and single Scheimpflug topographer data corresponded best. Similar trends were found at 8.0 mm. Test-retest variability hampered a detailed description of the anterior corneal shape at the level of individual subjects; interdevice variability compromises the exchangeability of the devices. No author has a financial or proprietary interest in any material or method mentioned.