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Ronald Ensing, Fleur de Lange, Harry de Vries, Michel Zaal, Victor Sicam; Clinical Validation of the Cassini Color LED Corneal Topography (CLCT) in post penetrating keratoplasty (PKP). Invest. Ophthalmol. Vis. Sci. 2013;54(15):528.
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© ARVO (1962-2015); The Authors (2016-present)
To report results of a clinical investigation involving comparison of corneal aberration measurements of CLCT with conventional Placido based and Scheimpflug based topographers.
23 PKP eyes from 16 subjects (age: 58 years ± 14 years, ranging from 35 to 81 years, 9 OD and 14 OS) were measured by three instruments: Cassini (i-Optics BV, The Hague, The Netherlands), OPD Scan (Nidek, Gamagori, Japan) and Pentacam (Oculus, Wetzlar, Germany). Corneal aberrations (Zernike Convention at 6 mm corneal zone) were compared. An artificial toric surface with gold standard measurement of 2.22 Diopter was also measured to assess the accuracy of the instruments. The standard deviation of three trials for every eye measurement was used to characterize precision of the instrument. The measurement with median defocus was used for inter-instrument comparison. The paired student’s t-test was used on the median data to find statistically significant differences.
Nidek OPD measures astigmatism of the toric surface with 2.7% error while CLCT measures the toric surface with with 0.5% error. The Pentacam has a precision reaching a mean of 0.25 μm for astigmatism measurements. Both the OPD and CLCT do not exceed a mean of 0.096 μm of precision in the measurement of corneal aberrations. Statistically significant differences have been found between the Cassini and the OPD for astigmatism (p = 0.0292) and quadrafoil (p = 0.0281) aberrations. The spherical aberration measured with Pentacam was significantly different from both Cassini and OPD (p = 0.0114 and p = 0.0194 respectively).
The lower accuracy of the OPD in measuring rotationally non-symmetric aberrations such as astigmatism and quadrafoil, can be explained by the fact that rings are used in the measurement. The use of rings does not measure the irregular features of the cornea accurately. The poorer repeatability of the Pentacam is a result of motion artifacts during acquisition. The Cassini and the OPD have comparable repeatability because it takes instantaneous measurements and is therefore not affected by motion artifacts. Among the three instruments, the Cassini measures corneal aberrations both accurately and precisely.
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