Shape of the anterior cornea: comparison of height data from 4 corneal topographers.
OBJECTIVE
To compare the ability of clinical corneal topographers to describe the shape of the anterior cornea for optical modeling.


METHODS
University Medical Center Groningen, Groningen, Netherlands.


METHODS
Cross-sectional study.


METHODS
The anterior corneal shape of healthy subjects was assessed with 4 topographers (Atlas Placido 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.


RESULTS
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 0.42 μm 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.


CONCLUSIONS
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.


BACKGROUND
No author has a financial or proprietary interest in any material or method mentioned.
From the Department of Ophthalmology (de Jong, Koopmans, Jansonius), University Medical Center Groningen, University of Groningen, Groningen, and the Department of Physics and Medical Technology (Dubbelman), VU University Medical Center, Amsterdam, Netherlands the National University Ireland-Galway (Sheehan), Galway, Ireland.
Tim
T
de Jong
Matthew T
MT
Sheehan
Michiel
M
Dubbelman
Steven A
SA
Koopmans
Nomdo M
NM
Jansonius
D000328:Adult; D001251:Astigmatism / Q000175:diagnosis; D003315:Cornea / Q000033:anatomy & histology* / Q000502:physiology; D019781:Corneal Topography / Q000295:instrumentation*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012029:Refraction, Ocular / Q000502:physiology; D015203:Reproducibility of Results; D055815:Young Adult