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Cassini topographer shows parity with other devices
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A novel keratometer with colored light-emitting diodes generated cylinder measurements comparable to those obtained with Placido rings, monochromatic LEDs and Scheimpflug images, according to a study.
The Cassini topographer (i-Optics), which analyzes corneal shape based on the reconstruction of specular reflections on 679 colored LEDs, generates keratometry and measurements of lower- and higher-order corneal aberrations.
The prospective study included 63 eyes of 63 subjects who underwent evaluation with the Cassini corneal topographer, Keratron (Optikon), Lenstar (Haag-Streit) and Pentacam (Oculus). Measurements were repeated three times with each device.
Corneal power measurements taken with the Cassini were statistically similar to those taken with the Pentacam but were significantly lower than those taken with the Keratron and Lenstar (P < .01). However, the differences had little clinical relevance.
Cylinder measurements taken with the Cassini were statistically similar to those taken with the other devices.
Repeatability of corneal power measurements taken with the Cassini was similar to that of measurements taken with the Keratron but was significantly lower than those taken with the Lenstar and Pentacam (P < .001).
The repeatability of cylinder measurements taken with the Cassini was significantly higher than that of cylinder measurements taken with the Pentacam and Keratron (P < .001) but did not differ significantly from measurements taken with the Lenstar. - by Matt Hasson
Disclosures: Klijn reports no relevant financial disclosures. Reus reports he receives research support and lecture fees from i-Optics. Sicam reports he is an employee of and holds patents from i-Optics.
Perspective
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Noel A. Alpins, MD
This paper examined the repeatability of corneal power and cylindrical measurements of a colored LED corneal topographer (Cassini) with comparisons to others using Placido, Scheimpflug and monochromatic LEDs.
Corneal power showed some differences between devices, but cylindrical magnitudes were not different from each other. Comparisons were only made between devices but not to a common standard such as refractive cylinder, which would have been helpful to display any difference in accuracy. Vector differences between measurements were significant, but summated vector means (centroid) were close to zero, suggesting measurement variability was random.
Mean axis is not a valid or useful analysis as the magnitude is not considered and steep meridians at 0° or 180° average 90°, which is inaccurate.
CorT, a parameter that shows the least variability in corneal astigmatism regardless of the device it is calculated on, could have been considered for accuracy in toric IOL implantation and LRIs. As it stated in this paper, most differences between devices were not significant. The posterior corneal effect on corneal astigmatism was not assessed.
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