Eyeworld

EW CATARACT 80 January 2017 by Maxine Lipner EyeWorld Senior Contributing Writer with an OVD rather than balanced salt solution, we run the risk of hav- ing 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 cor- neal 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 refrac- tion for OVD is different, investiga- tors launched the study looking at six OVDs that are commonly used. Included in the study were 120 eyes, Effect viscoelastic can have on intraoperative aberrometry W hen employing intra- operative aberrometry, the type of ophthal- mic 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 Cal- ifornia, 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 de- vice was designed to work with bal- anced salt solution, not OVDs, Dr. Masket noted. "If you alter the index of refraction of the transmitting me- dium, 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 Eyeing IOL power accuracy 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 continued on page 82 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 mm Hg with an operative applanation tonometer." After investigators had the pressure set and the wound sealed, they took three aberrometry readings, ex- changed 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, Ab- bott Park, Illinois), Amvisc (Bausch + Lomb, Bridgewater, New Jersey), and ProVisc (Alcon). "Those are all very similar in their index of refraction and molecular weight," Dr. Masket said, adding that with those there were no significant differences com- pared to results seen with balanced salt solution. Three other agents that had a higher index of refraction were also investigated, with a different outcome. "The index of refraction for the three prior agents was quite similar to balanced salt solution and therefore the results were similar," Dr. Masket said. When investigators looked at Healon GV (Abbott Med- ical Optics), Amvisc Plus (Bausch + Lomb), and DisCoVisc (Alcon), which have a higher index of re- fraction, it was a different story. The DisCoVisc and Amvisc Plus, which have a similar index of refraction, both turned out to have a statisti- cally significant difference in optical outcomes from balanced salt solu- tion, Dr. Masket reported. With the Healon GV, there was a trend toward a difference noted, but this was not statistically significant.

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