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J.C. He, R. Watanabe, J. Gwiazda; The Accuracy of Three Optical Systems in Measuring Corneal Wavefront Aberrations . Invest. Ophthalmol. Vis. Sci. 2006;47(13):562.
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© ARVO (1962-2015); The Authors (2016-present)
To test the accuracy of three optical systems in measuring corneal aberrations using either calibration of model eyes or comparison of data from the human eyes.
: The accuracy of a Humphrey Corneal Topographer System ATLAS 995 (Carl Zeiss Medtec, Inc) and an E300 Corneal Topogragher (Medmont International Pty Ltd) was tested by using these systems to measure both spherical aberration and x–axis coma for six aspheric standard surfaces (Sterling International Technologies, Inc) rotated 0 and 4.5 deg. along the x–axis. The accuracy of the Pentacam (Oculus, Inc) was tested by measuring Zernike aberrations for 26 young adult subjects (aged from 21 to 35 yrs and with mean Rx of –1.46D) and comparing the results with those obtained from the Humphrey ATLAS.
Relative to the predicted spherical aberrations with or without tilt, both the ATLAS 995 and the E300 provided over–estimates for all six surfaces with mean differences of 0.08 (44%) and 0.06 (32%) microns respectively. As predicted, no significant coma was detected in both systems when model surfaces were not tilted. With 4.5 deg. x–axis tilt, the measured x–axis comas with both systems were very close to the predicted values for five of the six surfaces. For the other surface (apical radius of 7.8 mm and shape factor of 1.3), over–estimates were observed for both the ATLAS 995 (25%) and the E300 (42%). The results from 26 subjects showed significant correlations between the CTS 995 and the Pentacam for astigmatism in 45/135 deg. (r=0.90, p<0.0001), astigmatism in 0/90 deg. (r=0.94, p<0.0001), y–axis coma (r=0.77, p<0.001), x–axis coma (r=0.87, p<0.001), and spherical aberration (r=0.53, p<0.01), but not for trefoils (r=–0.11 for Z6 and r=–0.14 for Z9). No significant difference between the two systems in the means was observed for the two astigmatism terms, two coma terms and the trefoil Z9. While a significant amount of the trefoil (Z6) was detected for this group of subjects with the ATLAS 995 (mean = –0.07 micron, t= 2.77, p<0.01), the mean was not significantly different from zero for the Pentacam.
Accurate measurement of higher order aberrations was partially achieved for both the ATLAS 995 and the E300. For the two systems, careful calibration will be needed to improve accuracy by compensating the systematic errors for some aberration terms. The Pentacam has compatible accuracy with the ATLAS 995 for all aberration terms evaluated except the trefoils.
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