EyeWorld India December 2013 Issue

December 2013 10 EWAP FEAturE Picture-perfect preoperative registration by Maxine Lipner EyeWorld Senior Contributing Writer Eyeing methods to align the toric IOL meridian T oric lenses are increasingly becoming a vital part of many practitioners’ armamentariums. New preoperative registration systems seek to align the toric meridian to preoperative landmarks on the eye. From self-directed iris fingerprinting to automated limbal registration systems such as the SensoMotoric Instruments guidance system (Verion, Alcon, Fort Worth, Texas, USA), the TrueVision 3D Surgical system (Santa Barbara, Calif., USA), iTrace (Tracey Technologies, Houston, Texas, USA), and Callisto Eye and Z Align (Carl Zeiss Meditec, Jena, Germany), EyeWorld examined what practitioners can expect from such systems. Fingerprint shots From the beginning, when toric lenses were introduced in the U.S., Robert H. Osher, MD , professor of ophthalmology, University of Cincinnati, and medical director emeritus, Cincinnati Eye Institute, Cincinnati, Ohio, USA, recognized that they were eventually going to become the standard of care, but there would be a lot of challenges. Iris fingerprinting was his first attempt to enhance accuracy. “I got frustrated with the fact that ink marks would diffuse 5 degrees, 10 degrees, 15 degrees, and sometimes they would entirely disappear,” Dr. Osher said. “It was necessary, in my opinion, to come up with some alternatives that would be more reliable.” Accordingly, he took pictures at the slit lamp when the pupil was dilated during the initial examination. This photograph was overlaid with a software protractor which, he observed, would tell him where every single degree mark was in relation to the unique iris anatomy. “Every landmark I was looking for on the iris corresponded to a specific degree,” Dr. Osher said. “I have total confidence that I can find my way around the eye and nail the target meridian,” he explained. With the fingerprinting technique, he has had outcomes on the first postoperative day of between 60 and 70% uncorrected 20/20 visual acuity. Systems with software to apply the fingerprinting technique include the Osher Toric Alignment System (OTAS, Haag- Streit, Koeniz, Switzerland) and Micron Imaging Systems (Pegram, Tenn., USA). SMI close-up Dr. Osher, who had the first SMI unit in the U.S., has considerable experience with this surgical guidance system, which he explains works by a whole different principle. “There is a preoperative unit that captures an image of the limbus, which is registered on a chip,” he said. “In the operating room this sophisticated technology allows the surgeon to select the degree of the target meridian, which then ‘guides’ the IOL rotation until perfectly aligned.” As Sonia Yoo, MD , professor of ophthalmology, Bascom Palmer Eye Institute, Miami, Fla., USA, who also has experience with the SMI system, explained it, the system takes a picture of the anterior segment, as well as topography. It is also linked with the operating room microscope, actively offering information while you’re operating. “The nice thing about the SMI system is that intraoperatively you have an active axis that moves based on where your lens is,” Dr. Yoo said. “You can see where your lens is sitting as you’re doing surgery and make adjustments as needed.” Dr. Osher believes that both the SMI unit and his iris fingerprinting technique are better than the traditional method of “guesstimating” with ink marks. iTrace shows digital topography overlay on the pupil. The yellow arrows here show man- ual ink marks made freehand attempting to mark 0 and 180 degrees. The marks are 15 degrees off axis temporally and 5 degrees off axis nasally. Source: Sonia Yoo, MD AT A GLANCE • With iris fingerprinting, a software protractor is overlaid on a photograph, allowing practitioners to see where every degree mark in relation to an iris landmark is located and ultimately nail the target meridian. • The SMI system memorizes the anatomy prior to surgery and then is able to automatically identify the target meridian. Intraoperatively it offers precise guidance during toric lens rotation. • With the iTrace system, a photograph of the cornea and limbus is overlaid with topography. Based on anatomic landmarks, physicians can mark the axis of astigmatism. • The Callisto Eye and Z Align gives a red-free photograph showing the vessels of the conjunctiva and limbus, which are imported to a computer connected to the microscope and laser system to help fine-tune lens positioning. • The TrueVision system optimizes wound placement and automatically registers the preoperative topography data and an eye image to the live 3D view of the eye, enabling digital guidance overlays with eyetracking for toric IOL alignment. • Intraoperative aberrometry can offer a real-time refractive solution that may eliminate the necessity of preoperative diagnostics.