EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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38 EW FEATURE February 2011 Diagnostic technologies for cataract surgery August 2013 How intraoperative aberrometry improves toric IOL implantation by Vanessa Caceres EyeWorld Contributing Writer AT A GLANCE • Intraoperative aberrometry makes toric IOL implantation easier and more accurate. • A hardware upgrade called VerifEye will further refine and improve the ORA intraoperative aberrometry technology, making it faster and more effective in real time. • The Holos intraoperative aberrometry system is under development. • One challenge with intraoperative aberrometry is maintaining patient centration and cooperation. Surgeons state how it's helped, where it will improve in the future I ntraoperative aberrometry has made toric IOL implantation easier. "With traditional methods of alignment for toric IOLs, while the refractive results are good, there is no way to be certain that the optimal refractive result has been achieved at the time of surgery," said Bret L. Fisher, MD, medical director, Eye Center of North Florida, Panama City, Fla. "With intraoperative aberrometry, there is real-time confirmation of both the sphere and cylinder, allowing a greater degree of precision in cataract surgery. This translates directly to improved outcomes and improved patient satisfaction." "The potential benefit of intraoperative aberrometry for toric IOLs is not only to determine or confirm the correct astigmatic power. It also lets the surgeon determine or confirm the proper axis, and in particular allows the surgeon to make a final intraoperative adjustment of the toric IOL alignment," said David F. Chang, MD, clinical professor of ophthalmology, University of California, San Francisco. Intraoperative aberrometry also incorporates posterior corneal astigmatism, said Sydney L. Tyson, MD, Vineland, N.J. "If not accounted for, posterior corneal astigmatism can lead to overcorrection for with-the- rule astigmatism and undercorrection for against-the-rule astigmatism," he said. Although the half diopter of astigmatism it usually accounts for may not seem like much, that small amount can lead to patient dissatisfaction in premium IOL patients. "The more we can stack the deck in our favor, the better," he said. Dr. Chang agrees. "Once we determine from preoperative keratometry that the cylindrical axis is 170 degrees, there are several new technologies to help us identify the 170 degree axis intraoperatively. However, such a system would miss three sources of error: posterior corneal astigmatism, surgically induced astigmatism from the incision, and tilting or head misalignment on the part of the technician who did the preop testing. Wavefront aberrometry will factor all of this in measuring the net refraction for the entire eye," he said. "Another advantage might be when there is discordance between different anterior corneal measurements, for example, keratometry and topography. A wavefront aberrometer is generating the best-fit refraction across the entire pupillary axis, just as our brain does during the postop refraction," Dr. Chang explained. Short of using the Light Adjustable Lens (Calhoun Vision, Pasadena, Calif.) for toric correction three weeks postoperatively, Dr. Chang believes that intraoperative aberrometry should provide the best prediction for toric IOL alignment and power. Holos wavefront aberrometer on a model eye with toric trial lens. Figure 1A shows 2.0 D of residual astigmatism at axis 98. The instantaneous real time refraction (quantitative) is displayed at the bottom of the screen. As a qualitative display, the red line shows the astigmatic axis, and the overlapping green line shows the amount of astigmatism. How aberrometry helps in the OR A number of cataract surgeons use the ORA wavefront intraoperative aberrometry system (WaveTec Vision, Aliso Viejo, Calif.). However, new aberrometry possibilities are on the horizon as ORA undergoes a hardware upgrade and as other aberrometers enter the market. Surgeons would also like more evidence to show that its use can improve surgical outcomes with toric IOLs. At least one study presented at the ASCRS•ASOA Symposium & Figure 1B shows the effect of rotating the toric trial lens. The instantaneous real time refraction (quantitative) is now emmetropic, and the qualitative display shows a new axis, and the green line is virtually gone indicating near elimination of residual astigmatism. Source: David F. Chang, MD