CATARACT EWAP DECEMBER 2022 9 sure that every patient is at least using lubricating drops prior to biometry and has a greater likelihood of having an ocular surface that is pristine and not dry.” For accurate measurements, Dr. McCabe suggested having a way to reliably and accurately obtain the corneal curvature/ Ks, noting there are several technologies for this. She also said it’s important to have an idea about the shape of the astigmatism, if it’s irregular, indicating a complex cornea, or regular astigmatism. “You don’t have to get super sophisticated about that, but you do need a picture of the central curvature of the cornea that tells you whether the astigmatism is regular or not,” she said. This can be determined with a topographer or even manual keratometry, looking for clear, sharp, and orthogonal mires. Having this basic information, Dr. McCabe said, helps set surgeons up for successful astigmatism treatment. Then you have to decide how to treat. There are several reasons that many physicians lean toward putting in a toric lens, if it’s indicated, she said. First, there is long-term stability and predictability of toric IOLs. “We don’t have to factor in healing of the arcuate incision, healing that’s individual to the patient,” Dr. McCabe said. Second, this option doesn’t impact ocular surface health, while arcuate incisions and cutting through the corneal nerves can worsen dry eye in the postoperative period. For these reasons, Dr. McCabe said she uses a toric lens when indicated, however, she noted that, in the U.S., low power torics are not available. “There are lower levels of astigmatism that I still think are important to treat, especially if we’re putting in a diffractive optic, and in those cases where it’s a lower level of astigmatism, I’ll do arcuate incisions,” she said. “I think allowing patients to have the best quality of vision at distance is what they find to be most important,” she said. “We can provide an increased independence with excellent distance vision for most patients, and that fundamentally depends on accurate and universally applied astigmatism correction.” The effect of residual astigmatism was the subject of an extensive study1 in which Dr. Schallhorn participated, looking at different amounts of astigmatism to determine what effect they have. “Above a relatively low level, you should consider addressing it to achieve the best unaided postoperative vision and maximize patient satisfaction,” he said. Dr. Schallhorn’s study found that even low levels of postoperative astigmatism can impact unaided vision and patient satisfaction after surgery. This includes 1 D or 0.75 D, but even down to 0.25–0.5 D. He called this conclusion a “wakeup call” for physicians to pay closer attention to corneal astigmatism and how to best address it. He also said that industry will play a big role in helping to develop better ways of correcting astigmatism, especially low levels. “Moderate to high levels of corneal astigmatism can be effectively addressed with toric IOLs, but if we want to raise the bar and improve outcomes, we need to refine methods to treat lower levels, both on the clinical side and on the industry side.” For example, Dr. Schallhorn said this could mean further developing and obtaining regulatory A s a preoperative evaluation of astigmatism, it is important to quantitatively evaluate the anterior and posterior corneal astigmatism and the condition of the cornea. In my opinion, the degree of astigmatism to be corrected for good postoperative visual acuity is 1.0 D or more for with-the-rule and against-the-rule astigmatism, and 0.75 D or more for oblique astigmatism. In addition, when using a multifocal IOL, residual astigmatism significantly affects postoperative visual acuity, so even preoperative corneal astigmatism of less than 0.75 D is carefully corrected. I also agree with Dr. Schallhorn that a slight hyperopic setting should be used to achieve good postoperative visual acuity. I developed the world’s first toric IOL in 19921, but it didn’t solve the problem of an average misalignment of 4 degrees, or about 12% undercorrection. Therefore, it is also important to work with this corrective effect in mind when using toric IOLs. Reference 1. Shimizu K, et al. Toric intraocular lenses: Correcting astigmatism while controlling axis shift. Cataract Refract Surg 1994; 20(5): 523-526. Editors’ note: Dr. Shimizu is a consultant for STAAR Surgical AG and KOWA. Kimiya Shimizu, MD Professor, Sanno Hospital 8-10-16 Akasaka, Minato-ku, Tokyo, Japan kimiyas@iuhw.ac.jp ASIA-PACIFIC PERSPECTIVES continued on page 12
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