Eyeworld

I N FOCUS 44 | EYEWORLD | AUGUST 2019 CATARACT SURGERY POST-LVC lean toward my biometry measurement (LENSTAR [Haag-Streit] or IOLMaster 700)." "Underlying dry eye syndrome or other oc- ular surface abnormality, such as EBMD, should be treated and optimized first," Dr. Devgan said. "The corneal topography and tomography give us a better idea of what is happening in the entire cornea compared to simple keratom- etry, which just gives us average corneal powers and astigmatism. I prefer the topography and tomography for determination of regularity, symmetry, and axis of astigmatism but will give more weight to keratometry from the optical biometer for the IOL power estimation." Dr. Koch recommends looking for evi- dence of the biometry's accuracy in the quality of the mires, the standard deviations of the magnitude and meridian, and the regularity of the cornea. "I will often remeasure, and for these cases will also use ORA [Alcon] in the operating room to help guide me, but there definitely are times that you don't get them to match, and you have to use your best judg- ment," he said. "It's not straightforward." "I usually measure patients two or three different ways—LENSTAR, IOLMaster 700, Galilei [Ziemer Ophthalmic Systems]—and we also have an OCT formula—we use the Avanti OCT [Optovue]," he added. Dr. Koch tries to develop a consensus based on all the data, leaning toward clustered measurements. Still, "sometimes going with the cluster doesn't get you the advantage you want," citing a recent case in which the cluster including ORA was 1 D off and the OCT formula was the only one that was accurate. Ultimately, he shows all patients—and those accompanying them—the variability of data from the ASCRS website calculations and explains that glasses, contact lenses, more corneal refractive surgery, or even an IOL exchange may be required to achieve the desired result. "That's just the reality of our imperfect science right now," he said. Dr. Devgan offered a final pearl: "When in doubt, choose the higher IOL power to err on the side of residual myopia, which provides a benefit for intermediate or near vision and if plano is desired, it is easy to treat with addition- al excimer laser ablation." The final outcome is also affected by the pa- tient's anatomy and healing response, he added. Meeting the challenge "Numerous strategies have been developed to account for the challenges of post-refractive surgery IOL calculations," Dr. Al-Mohtaseb said. She cited the ASCRS website, which provides current IOL power calculation for- mulas that have demonstrated effectiveness in post-LASIK eyes (ascrs.org). "There is no single formula that has been shown to be demonstra- bly better in all cases," she added. "Of the avail- able methods using no pre-refractive data, the Holladay 2, OCT IOL power formula, Barrett True K formula, and intraoperative aberrometry show promising results in comparative studies. I like using those three preoperative formulas in addition to the intraoperative aberrometry mea- surement before I make the final IOL decision." "With more than 20 different methods of IOL power estimation in post-refractive eyes, we know that none of them must be truly accurate across the board," Dr. Devgan said. "My preference is to use the ASCRS online post-refractive calculator and enter all of the data available to me. This calculator computes all possible formulae for which data has been supplied. This will give a range of values, most of which tend to agree. This agreement among multiple formulae is comforting but still not a guarantee of accuracy. Remember that in all eyes, the patient's healing response will affect the ELP and the refractive outcome." Of the current formulas, Dr. Koch favors the Barrett True K, the Haigis-L, and the OCT- based formula, available on ascrs.org. He also uses the Masket when prior refractive history is not available. A particular challenge that can arise is a discrepancy between biometry and topograph- ic keratometry measurements. "If there is a difference between biometry and topo Ks after optimizing the surface and making sure that the measurement quality is good, it is most likely due to the different location of measurements on the different machines (3-mm vs. 1.6-mm zones, for example)," Dr. Al-Mohtaseb said. "In those cases if there is a large difference in mea- surements, I would avoid putting in a toric lens or correcting astigmatism. I would most likely continued from page 43 Reference 1. Wang L, et al. Evaluation of total keratometry and its accuracy for IOL power calculation in eyes following corneal refractive surgery. J Cataract Refract Surg. Article in press. Financial interests Al-Mohtaseb: Alcon, Carl Zeiss Meditec, Johnson & Johnson Vision Devgan: www.IOLcalc.com, Advanced Euclidean Solutions, CataractCoach.com Gatinel: Alcon, Bausch + Lomb, Nidek, PhysIOL Koch: Alcon, Carl Zeiss Meditec, Johnson & Johnson Vision

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