EyeWorld India March 2017 Issue

42 March 2017 EWAP CATARACT/IOL by Maxine Lipner EyeWorld Senior Contributing Writer Eyeing IOL power accuracy Effect viscoelastic can have on intraoperative aberrometry W hen employing intraoperative aberrometry, the type of ophthalmic viscosurgical device (OVD) placed in the anterior chamber during phacoemulsification may affect the accuracy of the IOL power selected, according to Samuel Masket, MD , clinical professor, University of California, Los Angeles, and Advanced Vision Care, Los Angeles. In a study published in the Journal of Cataract & Refractive Surgery , investigators found that specific agents can affect optical results. 1 The aberrometry measuring device was designed to work with balanced salt solution, not OVDs, Dr. Masket noted. “If you alter the index of refraction of the transmitting medium, you’re going to impact what the device reads,” he said. With this in mind, investigators decided to take a closer look at the impact that OVDs could have on results. “I thought, ‘If we’re going to do this with an OVD rather than balanced salt solution, we run the risk of having an inaccuracy,’” he said. The reason some surgeons prefer an OVD in place of balanced salt solution is because practitioners learned early on that for repeatable and accurate readings they have to establish IOP at physiologic levels, Dr. Masket explained, adding that if there is a leaking incision, it’s hard to keep the pressure at a steady state. “In order to make sure the incision doesn’t leak, surgeons often will use a large degree of wound hydration,” he said. “If they do that to a great extent, they’re going to alter the corneal shape, leading to inaccuracy.” Some surgeons reasoned that filling the eye with OVD would eliminate the worry about wound leakage, and they could set the eye at physiologic levels and take the needed readings. Studying OVDs With this concern that there could be an error since the index of refraction for OVD is different, investigators launched the study looking at six OVDs that are commonly used. Included in the study were 120 eyes, with 20 placed in each OVD group. “The way we carried out the study, all incisions were done temporally, all were constructed with a 2.2-mm diamond blade and all IOLs were of the same basic platform—the Alcon SN series lenses [Alcon, Fort Worth, Texas], which could go through a D cartridge and a 2.2-mm incision,” Dr. Masket said. “After we removed the cataract and removed the cortex, we did careful stromal hydration and set IOP at 20 mmHg with an operative applanation tonometer.” After investigators had the pressure set and the wound sealed, they took three aberrometry readings, exchanged the balanced salt solution with the given OVD, and repeated the aberrometry readings. Then they prepared the aphakic refraction and the extrapolated IOL power, Dr. Masket said. Investigators found that the OVD agents studied fell into a few different categories. Among these were the low molecular weight 1% hyaluronic agents, which included Healon (Abbott Medical Optics, Abbott Park, Illinois), Amvisc (Bausch + Lomb, Bridgewater, New The ORA with VerifEye unit (Alcon). When determining IOL power for cataract patients with aberrometry, the type of viscoelastic physicians use can make a difference. View from the heads-up display as seen in the surgeon’s right ocular of the microscope Source (all): Samuel Masket, MD