EyeWorld India March 2019 Issue

EWAP FEATURE 11 Correcting corneal astigmatism by Ellen Stodola EyeWorld Senior Staff Writer/Digital Editor Experts discuss their preferences for managing corneal astigmatism C orrecting corneal astigmatism can be an important step in obtaining the best result for patients. This may be a factor both in cataract and refractive procedures. Several surgeons discussed how they determine corneal astigmatism, when they choose to correct it, and when they use different techniques—such as toric IOLs, LRIs, and femto AKs—to aid in the correction. Michael Greenwood, MD, Vance Thompson Vision, Fargo, North Dakota, Brandon Baartman, MD, Vance Thompson Vision, Omaha, Nebraska, Elizabeth Yeu, MD, Virginia Eye Consultants, Norfolk, Virginia, and Kevin M. Miller, MD, chief of the cataract and refractive surgery division, University of California, Los Angeles, discussed the correction of corneal astigmatism. Dr. Miller said that it is first important to identify whether a patient is presenting for refractive or cataract surgery. We handle these patients differently, he said. For the refractive surgery patient, Dr. Miller measures the manifest astigmatism using a phoropter. “It doesn’t matter what the corneal astigmatism is,” he said. The manifest astigmatism is what we treat, even if doing so increases the corneal astigmatism. For the cataract patient, it’s completely different. “We pay attention to what’s in the cornea and precisely measure the corneal cylinder. We can treat the corneal cylinder directly with relaxing incisions if it’s a small amount, or compensate for it by implanting a toric intraocular lens,” he said. “For cataract patients, we measure the corneal astigmatism and we don’t particularly care about the manifest astigmatism,” Dr. Miller said, adding that you can measure the front corneal surface with a variety of devices and infer the posterior corneal astigmatism, or you can measure the astigmatism on the front and back surfaces directly. Dr. Yeu said, “We’re very fortunate today that we have access to the Barrett toric calculator, and we have many years of experience and understand how refractive astigmatism affects vision.” She added that it’s important to differentiate between real and induced corneal astigmatism. “Identifying true corneal astigmatism will give us the best guidance in how to fix this at the time of surgery,” she said, adding that leaving more than 0.25 or 0.5 D on the table postoperatively can affect the quality of vision. Determining and correcting total corneal astigmatism Diagnostically, Dr. Yeu looks at several things. First, she uses a topographer to assess if it’s a good cornea capture. She uses the LENSTAR (Haag-Streit, Koniz, Switzerland) and captures between a 1.8- and 2.3-mm zone. Dr. Yeu also uses Cassini LED topography (Cassini Technologies, The Hague, the Netherlands) to see what is going on and to get instantaneous capture of the posterior cornea. In terms of how much she corrects, Dr. Yeu said that particularly for patients younger than 65, she aims to leave residual 0.25 D of with-the-rule astigmatism. “It will protect them as they may drift and will also give them a great outcome,” she said. For her patients who are 70 or older, she aims to leave them as astigmatically neutral as possible. Dr. Yeu said her trigger point for treating astigmatism is when there is any cylinder more than 0.2 D, especially if the patient is looking for a refractive outcome. She added it’s important for surgeons to get comfortable doing femto AKs and LRIs. For Dr. Greenwood’s preoperative measurements, he uses the LENSTAR and topography from the OPD-Scan III (Nidek, Fremont, California) to confirm that it is regular astigmatism. “My goal is to minimize any residual astigmatism, so I aim to correct the total amount of astigmatism,” he said. “I think that 0.50 D or more is visually significant.” Although there are some instruments that can estimate posterior corneal power, Dr. Greenwood thinks the most accurate way to measure total corneal power is intraoperative aberrometry, and for this, he is most familiar with using the ORA (Alcon, Fort Worth, Texas). Dr. Baartman said when he is evaluating a patient prior to cataract or refractive surgery, he takes into account the topography, Scheimpflug measurement of the posterior cornea, and the corneal wavefront measurements and compares them all to the magnitude and axis of manifest astigmatism. “When I’m considering toric lens placement, I like the Barrett toric calculator on the ASCRS website,” he said. “The amount of correction I would aim for depends on preoperative patient factors, such as pattern and regularity of the cylinder (e.g., is it with-the-rule or against-the-rule), and the presence of prior keratorefractive surgery or significant ocular surface disease.” Dr. Baartman said he generally starts considering correction when the patient has manifest cylinder that is present on topography, and his jumping-off point is about 0.5 D. Dr. Miller will use a Scheimpflug device to determine total corneal cylinder. He added he has both the Pentacam (Oculus, Wetzlar, Germany) and Galilei (Ziemer, Port, Switzerland) devices. Dr. Miller said a decision will be made on how to proceed after calculating the total corneal astigmatism/cylinder. He said he will treat any degree of astigmatism, and he likes to use the term “astigmatism management” when correcting small amounts because it’s not always possible to completely correct a patient’s astigmatism. When determining how much astigmatism to correct, Dr. Miller said it depends on where you want to land. His postoperative “sweet spot” is 0.3 D with-the-rule. AT A GLANCE • When managing corneal astigmatism, it’s important to know whether you’re dealing with a potential cataract surgery or refractive surgery patient. • When determining astigmatism, a variety of devices can be utilized, including topography, Scheimpflug technology, and LENSTAR. • Using the femtosecond laser for AKs can help with obtaining precise measurements. Toric IOLs are also good options for higher amounts of astigmatism. Continued on page 12 March 2019