EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/115557
100 EW FEATURE February 2011 Cataract/IOLs, femtosecond cataract March 2013 Managing postop refractive errors with premium IOLs by Vanessa Caceres EyeWorld Contributing Writer AT A GLANCE • Patient expectations are higher with premium IOLs, provoking the need to reduce postop refractive surprises in advance as often as possible. • Preop measurements with the use of reliable keratometry and modern-day biometry devices can help improve the refractive accuracy with IOL selection. • Surgeons should optimize the ocular surface before surgery to help avoid refractive surprises. • Postop refractive errors can occur in different forms with toric, accommodating, and multifocal IOLs. • Surgeons should especially take caution when implanting premium IOLs in patients with previous refractive surgery. Pearls to avoid (and better handle) post-surgery surprises T here's little room for forgiveness when you implant premium IOLs. "Patient expectations are higher any time a patient pays an out-of-pocket cost," said Terry Kim, M.D., professor of ophthalmology, Duke University School of Medicine, Duke University Eye Center, Durham, N.C. That said, unexpected refractive errors are bound to occur sometimes even for the most careful surgeons. Here's a review of some of the most common errors that anterior segment surgeons face with toric, accommodating, and multifocal IOLs and how to manage them—or how to avoid the problems altogether. Toric IOLs Because expectations are higher in premium IOL patients, Dr. Kim relies on accurate keratometry and biometry measurements during the preop assessment to try to avoid postop surprises. Preventive moves have led him and his practice to keep the rate of postop errors low, he said. "We get a corneal topography on these patients and also make sure the keratometry reading is reliable," he said. He said devices such as the The Toric Results Analyzer at www.astigmatismfix.com was developed to determine if a previously placed toric IOL is properly aligned. Lenstar LS900 (Haag-Streit, Mason, Ohio) and IOLMaster 500 (Carl Zeiss Meditec, Dublin, Calif.) that assist with biometry and keratometry are more accurate than they have been in the past. Surgeons should use a third- or fourth-generation IOL formula for biometry to help avoid refractive surprises as well, Dr. Kim said. In addition to the Holladay 2 formula, Dr. Kim recommends the Haigis or SRK-T formulas for axial lengths of greater than 25 mm; if the patient has an axial length of less than 22 mm, he prefers the Hoffer Q formula. Dr. Kim also makes sure that ocular surface irregularities—including dry eyes, blepharitis, anterior basement membrane dystrophy, and Salzmann nodules—are addressed prior to surgery, so they do not throw off the keratometry readings, which directly affect toric IOL calculations. "These conditions increase your chances of refractive surprises," he said. Residual astigmatism is the number one error faced by John Berdahl, M.D., Sioux Falls, S.D. when implanting toric IOLs. The first step he suggests is to find the cause of the astigmatism—it could be inaccurate keratometry, surgically induced astigmatism, the IOL is not in the ideal axis, there could be problems with the posterior corneal curvature, or the patient may have ocular surface disease, Dr. Berdahl said. Dr. Berdahl finds the most common cause of postop toric errors in his hands is underestimating the posterior corneal curvature. "You measure the anterior cornea and use that to determine the IOL, but you ignore the posterior cornea," he said. To better account for posterior corneal curvature as well as other factors, more and more surgeons are using intraoperative aberrometry, Dr. Berdahl said. Axis rotation occasionally happens in high-risk patients, such as those with large capsular bags or when the anterior capsule does not completely cover the optic edge, said Brad Black, M.D., Dr. Brad Black's Eye Associates, Jeffersonville, Ind. When encountering toric IOL issues, a number of ophthalmic surgeons now use a website called the Toric Results Analyzer (www.astigmatismfix.com) that was developed in the past year by Dr. Berdahl and David Hardten, M.D., Minneapolis. By comparing the toric IOL to the patient's current manifest refraction, the site can help determine if a rotation would decrease residual astigmatism. The site also provides the necessary amount of rotation. It takes good judgement to determine the value of performing postop fixes, Dr. Black said. "If a patient is happy and has good vision, we're hard pressed to intervene even if the IOL axis is not perfectly aligned with the intended axis," he said. If rotating a toric IOL, Dr. Black recommends loosening any and all adhesions of the capsule both to itself and the IOL using the viscoelastic of your choice. This often requires the use of a 27-gauge needle to very carefully initiate the separation of the capsular edge from the anterior surface of the IOL, Dr. Black said. He then suggests rotating the IOL a minimum of 180 degrees to make sure the haptics do not remain within a capsular sheath that might lead to postop rotation back to the unintended axis. To assist with alignment before surgery, Deepinder K. Dhaliwal, M.D., associate professor of ophthalmology, and director of cornea and refractive surgery service, University of Pittsburgh School of Medicine, will take the patient to the slit lamp and mark 12, 3, 6, and 9 o'clock using the slit beam and a marking pen. "I line up and mark the toric IOL axis based on my preoperative marks," said Dr. Dhaliwal, noting that she does not have access to intraoperative aberrometry. She'll also anesthetize and place betadine in the conjunctival fornices before marking to make sure the marks do not get washed out. "I have been very happy with the Lenstar for determining the magnitude and axis of astigmatism preoperatively," Dr. Dhaliwal said. Accommodating IOLs Not hitting emmetropia is a "necessary evil" when using accommodating lenses, Dr. Berdahl said. "The lens is intended to flex in the eye. The flexibility changes the lens position, so it results in more variable outcomes after surgery," he said. Although making postop corrections in this patient group is easy, the downside is that such enhancements take place fairly frequently, Dr. Berdahl said—in up to about 30% of his patients. A wait time of three months is reasonable for the lens to settle in the eye before deciding on enhancements, said the surgeons. Drs. Berdahl and Black prefer to do a YAG capsulotomy as necessary before enhancements as the YAG might change the refractive outcome. However, Dr. Black cautioned against doing a YAG if there's any concern that the IOL may need to be explanted. Dr. Dhaliwal has at times found stability issues with accommodating lenses. For this reason, she believes the use of a capsular tension ring is continued on page 102