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EW CATARACT 24 August 2015 Cataract editor's corner of the world by Ellen Stodola EyeWorld Staff Writer so far, studies have not verified that any machine is particularly accurate. The study of patients in his practice was done because soft- ware was implemented that allows tracking of outcomes of patients at a month after cataract surgery. He said that it's important to find those premium cataract surgery patients who are unhappy but who are not complaining. As collection of data began, Dr. Hovanesian said that satisfaction findings were correlated with other parameters in clinical outcomes. There was a clear correlation be- tween full correction of astigmatism and satisfaction, he said. In his practice, Dr. Hovanesian uses the ORA (Alcon, Fort Worth, Texas), which is a useful double- check of measurements. However, he said that having an aberrometer is not an excuse for not doing careful preoperative measurements. Dr. Hovanesian also has a Pentacam in his practice. There are 2 roles for these instruments, he said. The first is to determine whether there is an irregular cornea and if the anterior curvature is irreg- ular. The second role is to measure posterior corneal astigmatism; where that comes in is if the physician sees something very unusual in the posterior corneal astigmatism. "You don't have to have one of those instruments to do effec- tive astigmatism correction," Dr. Hovanesian said. But there will be better accuracy with it factored in. "I encourage every surgeon who's do- ing cataract surgery to think about astigmatism correction," he said. "It represents a lot of value added for patients. It's not hard to learn." The start-up cost is low, and satisfaction for patients is high. Although some doctors may not be comfortable with using presbyopia-correcting IOLs, astigmatism correction is a no-brainer, he said. EW Editors' note: Dr. Hovanesian has financial interests with Abbott Medical Optics (Abbott Park, Ill.), Bausch + Lomb (Bridgewater, N.J.), and Alcon. Contact information Hovanesian: jhovanesian@harvardeye.com error is determined by the central 2–3 mm of the cornea, he said. "We like to make sure the patient's eye doesn't rotate." Center the marks on the undilated pupil with the patient sitting upright, he recommended. Measuring posterior corneal astigmatism is important and can be done with the Galilei (Ziemer Ophthalmic Systems, Port, Switzer- land), Pentacam (Oculus, Arlington, Wash.), and Cassini (i-Optics, The Hague, the Netherlands) systems. Dr. Hovanesian said that 87% of eyes have "hidden" posterior astigmatism that acts like against-the-rule (ATR) of about 0.5 D. It does not drift with age, and for astigmatism planning, this can be added to the preexisting topographic astigmatism. If physicians correct on anteri- or topographic astigmatism alone, he said, for with-the-rule (WTR) astigmatism, the patient would be overcorrected by a half diopter, and ATR would be undercorrected by half a diopter. ATR tends to shift over time, with a shift of 0.4 D over 10 years, regardless of the patient's surgical status. In general, Dr. Hovanesian said the rule to follow if you use topog- raphy or Ks to plan surgery is to correct 0.5 to 0.7 D less than mea- sured Ks for WTR and to correct 0.5 D more than measured Ks for ATR. "Use the tools you have available in order to give patients the most satisfactory result," he said. Dr. Hovanesian followed up on the topic after his presentation, stressing the importance of posterior corneal astigmatism and how he personally uses it. "It's important to consider posterior corneal astig- matism 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. If you always make your incision at 180 degrees, you can disregard your SIA. If 90% of patients are half a diopter steep at 180 degrees and if a typical incision corrects a half diopter, then one cancels out the other, he said. In an ideal world, physicians would have a perfect way to mea- sure posterior corneal astigmatism, and some companies claim their instruments provide that with great accuracy, Dr. Hovanesian said, but It's important to factor in the role of the posterior cornea to ensure accurate measurements and patient satisfaction J ohn Hovanesian, MD, Laguna Hills, Calif., highlighted the role of the posterior surface in cataract surgery astigma- tism planning at the Hawaiian Eye meeting in Maui, Hawaii, in January 2015. Even a half diopter of astigma- tism can very much affect patient Handling posterior corneal astigmatism A ccuracy and precision with cataract surgical procedures is becoming the mainstay for most surgeries but particularly important when using a lens that helps with refractive outcomes. It has been known since the late 19th century that there exists a difference of approxi- mately –0.50 D x 90 between keratometric astigmatism, which measures the anterior corneal surface, and total refractive astigmatism. 1 Until recently, this was thought to be primarily due to lenticular astigmatism. However, studies have demonstrated this relationship in pseu- dophakic eyes, suggesting the discrepancy may be a result of the posterior corneal surface acting as a negative lens. 2,3 A recent study by Koch et al 4 provides evidence that posterior corneal astigmatism has a clinically important contribution to total astigmatism. Toric IOLs are becoming more common in use, and it is important to accurately calculate or predict the total corneal astigmatism. This is not always easy to do but recently has at least become more intuitive. In this article, John Hovanesian, MD, elegantly reviews the importance of and how to best approximate or measure total corneal astigmatism, including posterior corneal astigma- tism. He highlights the importance of good preoperative testing and calculations. I also refer the reader to the February 2015 edition of EyeWorld, where there are articles describing new IOL formula calculations taking posterior corneal astigmatism into account and new intraoper- ative aberrometry capabilities to help us determine the best lens for the patient. We continue to unravel the mysteries of the corneal and refractive outcomes as we aim for better outcomes for our patients. References 1. Javal E. Mémoires d'Ophtalmométrie: annotés et précédés d'une introduction. Paris, France, G. Masson, 1890;131. 2. Teus MA, Arruabarrena C, Hernandez-Verdejo JL, Sales-Sanz A, Sales-Sanz M. Correlation between ker- atometric and refractive astigmatism in pseudophakic eyes. J Cataract Refract Surg 2010;36:1671–1675. 3. Bae JG, Kim SJ, Choi YI. Pseudophakic residual astigmatism. Korean J Ophthalmol 2004;18:116–120. 4. Koch DD, Ali SF, Weikert MP, Shirayama M, Jenkins R, Wang L. Contribution of posterior corneal astigmatism to total corneal astigmatism. J Cataract Refract Surg. 2012; 38:2080–7. Rosa Braga-Mele, MD, cataract editor satisfaction, he said. A survey of 200 patients undergoing cataract surgery in his practice indicated that for patients with less than half a diopter of astigmatism, 80% were extremely satisfied, but this number dropped to 56% being extremely satisfied when the astigmatism was greater than 0.5 D. It's important to get the right measurements, and knowing your surgically induced astigmatism (SIA) aids in this, he said. Knowing the patient's corneal astigmatism is equally essential. Dr. Hovanesian noted that astigmatism is best mea- sured in the central 2 mm. Refractive

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