The Cassini topographer (i-Optics), which analyses corneal shape based on the reconstruction of specular reflections on 679 coloured LEDs, generates keratometry and is the new machine being compared in this study with other keratometry devices. The prospective comparative study included 63 eyes of 63 subjects who underwent evaluation with the Cassini corneal topographer, Keratron (Optikon), Lenstar (Haag-Streit) and Pentacam (Oculus). A power calculation was done to calculate the minimum sample size for the study. Measurements were repeated three times with each device. Patients who were booked to undergo cataract surgery and healthy volunteers were included in the study. Those with any kind of corneal problems were excluded under strict criteria. Parameters measured were corneal power and corneal cylinder. 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 and cylinder measurements taken with the Cassini was found to be significantly lower in terms of the corneal power when compared to other devices, but the cylinder power was significantly higher as compared to Pentacam and Keraton and similar to Lenstar. The comparability and repeatability was measured with other devices and the Cassini was found to be comparable to all. The corneal power measurement was noted to be slightly lower than the others. The repeatability was also found to be statistically significantly lower than the other devices in terms of the corneal power but higher in terms of the cylinder vector. Further studies with larger numbers will need to be done to see if they make a difference in normal and diseased corneas especially in the keractasia group of patients. 

Evaluation of keratometry with a novel color LED corneal topographer.
Klijn S, Reus NJ, Arni V, Sicam P.
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Mrinal Rana

University Hospital Coventry, Coventry, UK.

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