EyeWorld India June 2015 Issue

55 EWAP DEVICES June 2015 by Michelle Dalton EyeWorld Contributing Writer Using intraoperative aberrometry to improve astigmatic outcomes Improving preop measurements and using intraoperative ones is imperative, experts say I ntraoperative aberrometry— the ability to measure aphakic refraction during cataract surgery—is still in its infancy, but those who are using it say they are now within 0.5 D of target upward of 95% of the time, even with toric cases. Currently in the U.S., the ORA system (Alcon, Fort Worth, Texas) and the Cassini Total Corneal Astigmatism (i-Optics, The Hague, the Netherlands) are approved for use. The HOLOS IntraOp (Clarity Medical Systems, Pleasanton, Calif.) had a limited introduction for clinical use in early 2014, with full commercial release anticipated in the second half of 2015, according to the company. There are also other systems available outside the U.S. “The concept of correcting astigmatism seems simple enough, but as we get more involved with it, it becomes more complicated,” said Kerry Solomon, MD , in practice at Carolina Eyecare Physicians, Mount Pleasant, SC. Preoperative testing has been imprecise, surgically induced astigmatism occurs, and knowing how much astigmatism and on which axis it falls has been equally imprecise, said Stephen S. Lane, MD , medical director of Associated Eye Care, and adjunct clinical professor, University of Minnesota. Being able to measure the total corneal astigmatism (accounting for both anterior and posterior corneal curvature) is helping improve outcomes, and “we now know posterior corneal astigmatism may be very small in some patients and may be very significant in others. There’s really no easily and readily available way to know precisely preoperatively,” Dr. Lane said. “Both magnitude and direction are crucially important when you’re trying to measure corneal astigmatism.” For Dr. Solomon, the more information he can glean preoperatively, the better, including multiple keratometry measurements. “Up until recently, all of our measuring and testing for corneal astigmatism has been based on measurements before surgery that provide insufficient information for the physician to make a good decision,” he said. “It’s no wonder that our outcomes from corneal astigmatism are so variable.” Determining the true total preop corneal astigmatism is crucial, lest the amount of corneal astigmatism is being offset by the amount of lenticular astigmatism that would go unnoticed until measured in the aphakic state. Conversely, some patients will have natural lens-induced astigmatism that does not need a toric lens once the crystalline lens is removed. Dr. Solomon said before using intraoperative aberrometry, he was within 0.5 D “about 60% of the time using the Alcon toric calculator. Even after switching to the Holladay toric calculator, my outcomes only improved to 70%. Once I added intraoperative aberrometry, I’m within 0.5 D 89% of the time with toric implants.” The paradigm shift Historically, surgeons have used blue ink marks to determine the axis in toric intraocular lens surgery. “Blue ink marks run, they’re messy, they dissolve, they’re not very accurate,” Dr. Solomon said. “Quite honestly, in 2015, we can do better than blue ink marks.” Even when the ink is in the exact 3 o’clock and 9 o’clock positions, “people can be off 10 degrees or more because they don’t know what part of the ink mark to use as the exact reference point,” Dr. Lane said. “Aberrometry allows us to continue to take measurements throughout the surgery to ensure our measurements and calculations are correct.” Aberrometry also helps surgeons determine the amount of rotation that may be needed after a toric lens is implanted. Surgeons can “totally discount” any effect the crystalline lens had on astigmatism because total eye astigmatism can now be calculated with intraoperative aberrometry during the aphakic state, he said. Learning curves Both surgeons acknowledged that there are learning curves associated with the device, and physicians should not forego obtaining preop measurements. These devices have been designed to analyze the preop data surgeons input with measurements taken during the aphakic stage— and will alert surgeons if the two readings are not reasonably comparable, Dr. Lane said. “The two sets of readings don’t need to match up exactly, and oftentimes they do not, but they should be within 0.5–0.75 D of each other in cases where the corneas have not previously been altered,” he said. Dr. Solomon cautioned surgeons not to rely entirely on the intraoperative aberrometry— factors affecting potential outcomes (such as dry eye or ocular surface disease) need to be addressed before surgery and could influence the reading intraoperatively. “In surgery, there are a number of little tricks to make sure you’re doing the right thing: keeping the lids and lashes out of the way, making sure the cornea is moist, making sure the intraocular pressure is what it needs to be to take the measurement, minimizing or avoiding stromal hydration of the cornea, which can affect the measurements, keeping the continued on page 56