Eyeworld

EW CORNEA 126 October 2016 by Michelle Dalton EyeWorld Contributing Writer Orbscan 3 The Orbscan 3 (Bausch + Lomb, Bridgewater, New Jersey) is being introduced this month and uses slit scan technology with "an advanced Placido disk system," the company said. The resolution is significantly higher than with previous models, providing 23,000 points of recogni- tion. Like other new topographers, the Orbscan 3 provides both anterior and posterior corneal elevation and curvature, full corneal pachymetry, white-to-white diameters, and pre- and postop difference maps. EW References 1. Klyce SD. Computer-assisted corneal topog- raphy. High-resolution graphic presentation and analysis of keratoscopy. Invest Ophthal- mol Vis Sci. 1984;25:1426–1435. 2. Shirayama M, et al. Comparison of accuracy of intraocular lens calculations using auto- mated keratometry, a Placido-based corneal topographer, and a combined Placido-based and dual Scheimpflug corneal topographer. Cornea. 2010;29:1136–1138. 3. Ambrosio R, et al. Imaging of the cornea: topography vs tomography. J Refract Surg. 2010;26:847–849. Editors' note: All information in this article is from public sources and websites. processing data point-by-point. This 5-in-1 system provides auto-refrac- tion, corneal topography, ray tracing aberrometry, pupillometry and auto-keratometry." By adding wavefront aberrome- try to corneal topography, the com- pany claims a "unique analysis" that isolates the internal aberrations of the eye by subtracting the corneal ab- errations from the total aberrations. OPD-Scan III The OPD-Scan III (Nidek, Gamagori, Japan) combines wavefront aberrom- eter, topography, auto-refractometer, auto-keratometer, and pupillometer/ pupillographer into one refractive workstation. This device separates the total, corneal, and internal component irregularities to help clinicians determine the source of the optical pathology. A retroillumination im- age of cataracts captured during the OPD exam allows better understand- ing of pupillary effects on vision and in patient education. According to Nidek, the 9.5 mm diameter measurement area "ensures full coverage of almost any pupil and provides 2,520 data points for wavefront aberrometry." Additional- ly, the device's 33 blue Placido mires "provide a minimum of 11,880 data points," and the company notes blue wavelength allows for greater precision in ring detection. for detecting subtle changes on the anterior corneal surface secondary to ectatic disorders. 3 In this month's "Device focus," EyeWorld provides an update from the manufacturers on the various topography systems currently available. Atlas 9000 Corneal Topography System The Atlas 9000 Corneal Topography System (Carl Zeiss Meditec, Jena, Germany) has a patented alignment system, and its ability to analyze multiple images during the align- ment phase means it will automat- ically select the highest quality image. A software element stream- lines gas permeable contact lens fittings as well as other difficult and specialty lenses. By using its pro- prietary "cone of focus" alignment system, the Atlas is said to deliver sub-micron elevation accuracy. The company touts the 22-ring Placido disk as being optimized to avoid ring crossover, resulting in more reliable results for a wide range of patients. In addition, its corneal analy- sis software anterior topographic screening tool assists with refractive surgery screening and helps identify abnormal corneal conditions for monitoring and follow-up. The device's corneal wavefront analysis "takes corneal topography to a new dimension. Using ray trac- ing technology, the Atlas displays higher-order corneal aberrations, providing valuable insight for patient education and treatment planning." Plus, by measuring the pupil size at both scotopic and photopic illuminations, the device can pro- vide insight into optical zones under varying light conditions. i-Trace The iTrace Ray Tracing Wavefront Aberrometer and Corneal Topog- raphy (Tracey Technologies, Hous- ton) "sequentially projects 256 near-infrared laser beams into the eye to measure forward aberrations, Some skeptics claim tomography has more benefits than topography, but both are needed in anterior segment surgery T hanks to technological advances, physicians are able to image the entire cornea, including the ante- rior and posterior cornea. Most topographers are Placido-based devices that primarily image the an- terior surface of the cornea, whereas tomography refers to Scheimpflug- based devices and some optical co- herence tomography (OCT) devices that become a 3D reconstruction of the anterior segment. Topography as used today was introduced in the 1980s, and Stephen Klyce, PhD, is largely credited with developing the maps produced that are derived from numerous points on the cornea. 1 Placido-based devices will also show tear film abnormalities, which Scheimpflug-based systems do not. The Placido-based devices have been shown to be as accurate in IOL power calculations on their own as automated keratometry or as a combined Placido-based and dual Scheimpflug corneal topogra- pher. 2 The data these devices provide must be extrapolated to determine anterior and posterior elevation and pachymetry, whereas the Scheimp- flug systems do not directly assess corneal curvatures. Some experts think topography is limited in that it can only image one surface of the cornea and only about 60% of that surface (that of the central cornea), and that to- mography and OCT provide images from limbus-to-limbus and have full pachymetry maps as well. Yet others think both topography and tomog- raphy are necessary in any burgeon- ing high-volume anterior segment practice. Corneal topography became an integral part of refractive surgery screening, known for its sensitivity Today's corneal topographers Device focus " Corneal topography became an integral part of refractive surgery screening, known for its sensitivity for detecting subtle changes on the anterior corneal surface secondary to ectatic disorders. "

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