Eyeworld

EW REFRACTIVE SURGERY 98 March 2015 by Michelle Dalton EyeWorld Contributing Writer Improving preop measurements and using intraoperative ones is imperative, experts say I ntraoperative aberrometry— the ability to measure aphakic refraction during cataract sur- gery—is still in its infancy, but those who are using it say they are now within 0.5 D of target up- ward 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, S.C. Preoperative test- ing 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 Asso- ciated 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 out- comes, 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 preoperative- ly," Dr. Lane said. "Both magnitude and direction are crucially import- ant when you're trying to measure corneal astigmatism." For Dr. Solomon, the more information he can glean preopera- tively, 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 deci- sion," he said. "It's no wonder that our outcomes from corneal astigma- tism are so variable." Determining the true total preop corneal astigmatism is crucial, lest the amount of corneal astigma- tism is being offset by the amount of lenticular astigmatism that would go unnoticed until measured in the aphakic state. Conversely, some pa- tients 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 in- traoperative 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 ex- act 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 measure- ments 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 astig- matism can now be calculated with intraoperative aberrometry during the aphakic state, he said. Learning curves Both surgeons acknowledged that there are learning curves associat- ed with the device, and physicians should not forego obtaining preop measurements. These devices have been de- signed to analyze the preop data surgeons input with measurements taken during the aphakic stage—and will alert surgeons if the 2 readings are not reasonably comparable, Dr. Lane said. "The 2 sets of readings don't need to match up exactly, and often- times 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 intraoper- ative aberrometry—factors affecting potential outcomes (such as dry eye or ocular surface disease) need to be addressed before surgery and could influence the reading intraopera- tively. "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 avoid- ing stromal hydration of the cornea, which can affect the measurements, keeping the lid speculum off the eye and out of the measurements. Those are things that can give you false readings from aberrometry," he said. Even if every step was per- formed perfectly, the intraoperative readings may at times differ sig- nificantly from the preop readings, especially if there is more edema, a prominent vitreous detachment, or prominent vitreous floaters. In those instances, Dr. Solomon will use his original preop measurements to guide IOL choice and alignment. Similarly, if the cornea is healthy and has never undergone surgery and there is still a large discrepancy between pre- and intraoperative readings, Dr. Lane will err on the side of caution and use his preop measurements to guide IOL choice. "But it's an extremely rare occurrence for the 2 to be drastically different," he said. During the initial learning curve, Dr. Lane said if there are discrepancies in the readings, "you can't go wrong by going with your preoperative measurements because that's what you've done your whole career. That's what we've all done our whole career." But there are always exceptions to the rule, Dr. Lane said, including the post-LASIK patient, where the preop and intraoperative measure- ments can vary by as much as 1.5 D. "Those are the patients that I use my intraoperative aberrometry measurement for, regardless of how far off the preoperative one might be, simply because of the inaccuracy of trying to use preoperative values and the changes that take place in terms of the cornea during LASIK," he said. For all others, if the readings do not concur, repeat the aberrometry readings, Dr. Lane suggested. Ensure the eye is properly pressurized, and "make sure that the speculum isn't pushing on the eye in a certain way that can induce astigmatism or change astigmatism. You want to make sure that the ocular surface is well moistened," he said. If the axis of astigmatism agrees pre- and intraoperatively but the lens power differs, Dr. Solomon typi- cally uses the intraoperative assess- ment. If, however, preop indicates with-the-rule and intraoperative sug- gests against-the-rule, Dr. Solomon is likely to use the preop measure- ments instead. That noted, "I throw out the intraoperative aberrometry measurement maybe 2% [to] 5% of the time. So 95% [to] 98% of the time, I find intraoperative aberrome- try to be accurate and helpful." Dr. Lane estimated that he changes his IOL powers about 50% of the time, "however, 90% of the time it changes by only 0.5 D or so," he said. "Intraoperative aberrom- etry has improved the percentage of patients that I'm able to achieve within ±0.5 D of target to about 94% of the time." EW Editors' note: Drs. Lane and Solomon have financial interests with Alcon. Contact information Lane: sslane@associatedeyecare.com Solomon: kerry.solomon@carolinaeyecare.com Using intraoperative aberrometry to improve astigmatic outcomes Device focus

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