Evaluation of Keratometry With a Novel Color-LED Corneal Topographer

Abstract

good refractive outcome in cataract and refractive surgery relies on accurate and precise keratometry, particularly in procedures to correct astigmatism. Erroneous keratometric measurements may be a source of intraocular lens (IOL) power calculation errors, 1,2 which lead to postoperative refractive surprises. In addition, appropriate measurement of cylinder axis is important in toric IOL implantation because every degree of misalignment reduces the corrective effect. 3,4The manual Javal-Schiøtz keratometer, invented in the late 19th century, has largely given way to a variety of automated keratometers. These devices employ different techniques to provide automated analogues of traditional, manual keratometry readings. Commonly used keratometers are based on reflections of Placido rings, reflections of monochromatic lightemitting diodes (LEDs), Scheimpflug images, or a combination of these. Although of proven clinical value, topography based on Placido rings holds the disadvantage of neglecting skew rays, 5 which may lead to inaccuracies in measuring features of the cornea that are not rotationally symmetric (eg, corneal cylinder). [6][7][8] This may be solved by using a corneal reflection source that allows for point-to-point reconstruction.9,10 Simulations have shown that such a technique might be more accurate and precise than topography based on Placido rings. METHODS: Sixty-three eyes of 63 patients with virgin corneas underwent keratometry with color-LED corneal topography (Cassini; i-Optics, The Hague, The Netherlands) and with devices based on Placido ring reflections (Keratron; Optikon, Rome, Italy), monochromatic LED reflections (Lenstar; Haag-Streit, Koeniz, Switzerland), and Scheimpflug imaging (Pentacam; Oculus Optikgeräte, Wetzlar, Germany). Three repeated measurements were performed with each device. Comparability and repeatability of corneal power and cylinder measurements were assessed. The Bonferroni-corrected α-threshold for statistical significance was 0.016. RESULTS:Corneal power measurements with the Cassini topographer were not statistically significantly different from those with the Pentacam (P = .64). They were statistically significantly lower than those with the Keratron and Lenstar (P < .01), but the differences were of negligible clinical relevance. Cylinder measurements with the Cassini topographer were not statistically significantly different from those with any other device (P = .46). Repeatability of Cassini corneal power measurements was not statistically significantly different from that of the Keratron (P = .02), but was statistically significantly lower than that of the Lenstar and Pentacam (P < .001). Repeatability of Cassini cylinder measurements was statistically significantly higher than that of the Pentacam and Keratron (P < .001), but was not statistically significantly different from that of the Lenstar (P > .05). CONCLUSIONS:Corneal power and cylinder measurements with color-LED corneal topography yielded values that were comparable to those of other commonly used d...

Comparative analysis of anterior corneal curvature and astigmatism measurements obtained with three different devices

“…The aim of the current study was to evaluate and compare the keratometric measurements provided by three different commercially available devices in healthy eyes in order to assess the level of interchangeability between them. Previous studies have reported the keratometric outcomes obtained with the Cassini, [9][10][11]13,17,18 Pentacam, 7,[19][20][21] and IOL-Master 22,23 systems in healthy eyes, confirming a good level of intrasession repeatability associated with such measurements. However, the present study is thought to be the first to report a comparison between these three devices.…”

“…These authors only obtained statistically significant differences between devices for J 0 (mean difference: 0.18 D). 30 Klijn et al 10 concluded in another comparative study that there were statistically significant differences between Cassini and Pentacam in terms of the magnitude of astigmatism, but not for the axis of the steepest corneal meridian. Chang et al 4 compared the astigmatic measurements obtained with Pentacam and IOL Master and did not find statistically significant differences between devices in the measurement of the magnitude of corneal astigmatism.…”

“…Another factor that may have contributed to the poor interchangeability between devices is the capability of each device used to provide consistent measurements. However, the levels of intrasession repeatability of keratometric and astigmatic measurements provided by Cassini, [9][10][11]13,17,18 IOL-Master 22,23 and Pentacam 7,[19][20][21] systems have been previously shown to be excellent, with no clinically relevant differences between repeated measurements with each device. Therefore, this factor may have contributed to the poor interchangeability between devices in the present study, but it cannot be a critical factor explaining this.…”

“…Specifically, the absolute value of this power vector component was higher when measured with IOL-Master compared to the Pentacam system. Comparisons between Cassini versus Pentacam, 10,30 and also between Pentacam and IOL-Master 4,31 have been previously performed. Apparently contradictory conclusions/results have been reported, although the ranges of agreement are consistent with those obtained in the current study.…”

“…5,8 New topographic devices should be compared with these reference devices in order to verify that similar or interchangeable measurements of basic parameters are obtained using them. Colour light-emitting diode topographers, such as the Cassini system from i-Optics, have been recently introduced and their results have been compared with those obtained with Placidobased topographers [9][10][11][12] and Scheimpflug imaging-based tomographers. 9,10 However, keratometric readings obtained with this device have not been compared with those obtained with the IOL-Master system.…”