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EW FEATURE 50 Toric IOLs June 2015 spherical power of the IOL in the final toric calculation," he said. Dr. Mah likes the fact that the 3 major companies with toric IOLs commercially available in the U.S. have toric calculators. "I think one thing that's im- portant for the beginning toric IOL surgeon is to use the commercially available toric IOL calculators," he said. Additionally, Dr. Mah uses the Barrett Toric Calculator, which is available on the ASCRS website. "As information becomes available, such as posterior corneal power, that can be adopted into the newer IOL calculators," he said. Alcon (Fort Worth, Texas), Abbott Medical Optics, and Bausch + Lomb (Bridgewater, N.J.) all have online calculators that are free, Dr. Hovanesian said. Although he generally does his own calculations, he said these calculators become valuable when there is an unusual angle. "They allow you to put in the patient's astigmatism, the intended lens, and the surgically induced astigmatism," he said. "What they do not include is the posterior cor- neal astigmatism." Posterior corneal astigmatism Posterior corneal astigmatism is something that a number of physi- cians are factoring into their mea- surements. This can be done with specific tools and also with a general estimate. To account for posterior corneal cylinder, Dr. Garg said he generally undercorrects with-the- rule cylinder and slightly overcor- rects against-the-rule cylinder. "I have recently started looking at the Barrett Toric Calculator, which takes into account posterior corneal cylinder," he said. "Additionally, I routinely use intraoperative aber- rometry for my toric IOL cases." Dr. Hovanesian said that pos- terior corneal astigmatism plays an important role for these patients. "It's important to consider posteri- or corneal astigmatism because for nearly 90% of patients there is about a half diopter of corneal astigmatism that behaves as though it is steep at 180," he said. Using an intraoperative wave- front aberrometry system like one from Clarity Medical Systems (Pleasanton, Calif.) or the ORA (Alcon) can measure all the aberrations of the eye, including posterior corneal astigmatism. There are a couple of ways to factor in posterior corneal astigma- tism, Dr. Mah said. Posterior corneal astigmatism can be calculated by using a diagnostic machine, or a physician can just incorporate the "fudge factor," which is around 0.5 D to 0.75 D, he said. "I think there's an impression that in order to start down the path- way of doing premium IOLs and toric IOLs, everyone has to invest in new equipment and spend a lot of money in order to get good results," Dr. Mah said. However, he thinks that good results can be obtained without some of these machines, although these technologies can be helpful in improving outcomes, he said. Toric IOLs are a benefit to patients, and surgeons need to look closely at adopting them, he said. EW Editors' note: Drs. Hovanesian and Mah have financial interests with Alcon, Abbott Medical Optics, and Bausch + Lomb. Dr. Garg has financial interests with Abbott Medical Optics. Contact information Garg: gargs@uci.edu Hovanesian: johnhova@gmail.com Mah: Mah.Francis@scrippshealth.org important to counsel patients about the astigmatism we are treating." Patients need to understand the difference between corneal astigma- tism and manifest astigmatism, he said. "I find it useful to show pa- tients their diagnostic tests so they understand that I am treating their corneal astigmatism, with a goal to minimize their refractive error," he said. Toric IOL calculator Although many physicians may be able to implant toric IOLs without the use of a toric calculator, this is another tool that can be used to ensure accuracy and can make measurements and preoperative assessments easier. "Figuring out toricity in a case that is on axis is not difficult," Dr. Garg said. "However, for patients whose astigmatism is not on axis the toric calculator is very useful." The determination of the final axis involves vector analysis. Dr. Garg prefers to use the Abbott Medical Optics toric calculator (Abbott Park, Ill.). "This calculator not only provides a choice of IOL powers but also compensates for the Succeeding continued from page 49 by Maxine Lipner EyeWorld Senior Contributing Writer AT A GLANCE • More than 0.5 D of residual astigmatism can be an unwelcome surprise for toric IOL patients. • Cumulative small errors may contribute to a significant toric surprise. • Toric surprise patients who cannot be corrected by a simple IOL rotation may have to undergo laser vision correction or an IOL exchange. comfortable. "Now you're prescrib- ing glasses in someone who thought they had bought an IOL to avoid glasses," he said. The only other options are to go back to the OR and rotate the lens or to do a secondary intervention with laser vision correction. Common causes Dr. Serafano finds that the most common cause of postoperative error is the result of small cumula- tive misses. "You give up 2 or 3 degrees on cyclotorsion, you give up a couple of degrees on your marking, and may- be when you put the IOL in, you remove the viscoelastic and you got a little movement of the lens and don't get it reoriented correctly," he said, adding that soon the surgeon is 8 or 10 degrees from where he or she would be in the mathematical calculations. of astigmatism is definitely an unwelcome one for both patients and practitioners. "I don't like a 4–5% surprise rate that results in more than 0.25 D of postoperative astigmatism," Dr. Yeu said. Here is a closer look at what causes such errors and what can be done to keep patients happy. Dr. Yeu finds that any rotation that is going to lead to more than 0.5 D of residual astigmatism is going to be visually significant for patients. This means that the more astigmatism that is being corrected, the less margin there is for error. For example, if a patient needs just 1 D of astigmatism correction, as long as about half of that is corrected, the patient will likely not have com- plaints. However, by contrast, if you are correcting 3 D of astigmatism, at least 2.5 D needs to be successfully treated, Dr. Yeu noted, adding that not too much rotation of the toric lens can be tolerated as that will leave residual uncorrected astigma- tism. Donald N. Serafano, MD, asso- ciate clinical professor, Department of Ophthalmology, University of Southern California, and Eye Phy- sicians of Long Beach, Long Beach, Calif., agreed that the amount of toric lens rotation tolerated by patients is small. "I think you will do well if they're (within) + or –4 degrees from the mathematical cal- culated axis," he said. If the lens is off axis by more than this, he finds that 2 things will occur. Not only will the patient lose the effect of the toric IOL, but also in vector analysis there will be resulting astigmatism at another axis. "It's not just a matter of a doctor saying, 'I was off and I didn't get as much effect as I thought I would,'" Dr. Serafano said. "You actually have produced an astigmatism somewhere else." This can be frustrating to the patient who now has some refractive astigmatism at some oblique axis, which is not Blowing out the candles on toric surprise Dealing with rotation, power problems, and more I t happens with no fanfare in about 1 out of every 20 to 25 cases—toric IOL surprise, ac- cording to Elizabeth Yeu, MD, assistant professor of ophthal- mology, Eastern Virginia Medical School, Norfolk, Va. But unlike some surprises, under- or overcorrection continued on page 52

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