EyeWorld Asia-Pacific September 2014 Issue

55 EWAP rEfrActivE September 2014 Views from Asia-Pacific Choun-Ki JOO, MD, PhD Professor Woong-Joo WHANG, MD Clinical fellow Department of Ophthalmology & Visual Sciences, Seoul St. Mary’s Hospital Eye Institute (SSEI) 222 Banpo-daero, Seocho-gu, Seoul 137-701 Korea Tel. no. +82-2-22586316 olokl@nate.com I ntraoperative aberrometry is an ideal tool for toric IOL selection. That reduces absolute refractive astigmatism and improves uncorrected vision. Prior studies showed statistical significance between the ORA—typical intraoperative aberrometry—and non-ORA group. Those results indicated a 57% reduction in cylinder in the non-aberrometry group, and in the aberrometry group there was 75% reduction in cylinder. However, cataract surgeons wouldencounter a practical problem. The system is hard to use and has a learning curve. Furthermore, it has an economic problem. It is too expensive to generalize in cataract surgery. So we must also improve the refractive outcomes of the standard method. First of all, investigating the reasons that make refractive error is needed and the main causes are supposed to be two factors: posterior corneal astigmatism and preoperative biometry. Traditionally, the difference in refractive indices between the cornea and aqueous is so small that the posterior cornea induces minimal refractive astigmatism and can be ignored in astigmatic calculations. However, several studies using different methodologies reported that the posterior corneal astigmatism that ranges from 0.26 to 0.78 D and Koch et al. concluded that corneal astigmatism was overestimated in with-the-rule (WTR) and underestimated in against- the-rule (ATR) astigmatism. To additionally consider the posterior corneal astigmatism, new keratometric measurements would be recommended. The Pentacam Scheimpflug camera provides true net power (TNP), total corneal refractive power (TCRP), and equivalent K-readings (EKR). Not only the anterior cornea but also the posterior cornea are applied for the calculation of those measurements via the Gaussian optic formulas and ray-tracing method. The application of axis measured by Pentacam rotating Scheimpflug camera considering the astigmatism of posterior cornea might be helpful to minimize the refractive cylinder. There is another factor to correct. In recent studies concerning toric intraocular lenses, Savini et al. demonstrated that the postoperative anterior chamber depth influenced the ratio between the cylinder power in the intraocular lens plane and the cylinder power in the corneal plane, and therefore should be accounted for when selecting a toric intraocular lens in an eye whose corneal power and axial length are far from the average values. Those results are calculated by theoretical IOL formulas and the investigations via optical bench testing or more accurate defocusing curve should be needed. Editors’ note: Drs. Whang and Joo have no financial interests related to their comments. placement was determined by an ORA system (Optiwave Refractive Analysis, WaveTec Vision, Aliso Viejo, Calif., U.S.) aphakic refraction. With the traditional method, the cylinder power and axis of placement was determined by standard biometry and the use of an online toric calculator. The primary outcome measurement was mean postoperative residual refractive astigmatism. The mean preoperative keratometric astigmatism in the aberrometry group was 1.83 D with a range of 0.74 D to 3.77 D. Meanwhile, in the non-aberrometry group, the mean was 1.59 D, with a range of 0.69 D to 4.1 D. Intraoperative aberrometry, including the ORA machine that Dr. Hatch uses, can help physicians make decisions in the operating room. She said that when using this tool, there was a change for toric and spherical IOL power 24% and 35% of time, respectively, in the operating room. “We can also decide whether we need to rotate the lens,” Dr. Hatch said. Two-thirds of the time, there was no need for additional rotation after the initial insertion, and 92% of the time less than three rotations were needed. This study showed statistical significance between the ORA group and the non-ORA group. She added there was a lower residual refractive astigmatism in the ORA group. “Across the board, the chance of patients being in lower postoperative residual refractive range increases when intraoperative aberrometry was used, and this was statistically significant,” Dr. Hatch said. She said that when conducting the tests on effectiveness of the intraoperative aberrometry, the results compared to the Alcon (Forth Worth, Texas, U.S.) FDA trial, which tested for similar results. Results indicated a 57% reduction in cylinder in the non- aberrometry group, and in the aberrometry group there was a 75% reduction in cylinder. There was a higher percentage of patients with better vision in the ORA group than in the non-ORA group, Dr. Hatch said. “You don’t always get it right the first time, and in our hands the ORA allowed us to make changes,” she said. “We did change one in four patients, we did change the power of the toric lens, and we did do a rotation in one in three patients.” Intraoperative aberrometry reduces absolute postoperative residual refractive astigmatism and improves uncorrected vision, Dr. Hatch said. “The take-home [point] is in our hands, patients were two-and- a-half times more likely to have less than half a diopter of astigmatism with the use of aberrometry,” Dr. Hatch said. She added the study has found that toric patients and those with higher degrees of astigmatism as well as post-LASIK patients tend to reap the benefits of ORA more than standard cataract patients and those who have had no prior surgery or have minimal astigmatism. Dr. Hatch said there can be some disadvantages of the ORA system, and it can take some getting used to. “It certainly does add operating room time,” she said. Cost is also a factor, as it is not covered by insurance. The system has a learning curve. Dr. Hatch said a surgeon has to become familiar with it and know when to trust the information that it’s giving. She started by using intraoperative aberrometry on routine cases, making sure that the measurements matched with her measurements. EWAP Editors’ note: Dr. Hatch has no financial interests related to her comments. contact information Hatch: kmasselam@gmail.com