OCT 2019

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

Issue link: http://digital.eyeworld.org/i/1171786

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Page 48 of 78

I WHAT OPHTHALMOLOGISTS SHOULD BE DOING TODAY N FOCUS 46 | EYEWORLD | OCTOBER 2019 by Chiles Samaniego EyeWorld Contributing Writer magnitude of the astigmatism, (2) to detect abnormal topography such as keratoconus, and (3) if one has a Placido device, to evaluate the ocular surface by examining the quality of the mires," he said. Dr. Raviv agreed that "every refractive sur- geon needs topography." He explained: "Biom- eters only give two Ks and a steep axis and it's critical to see the whole picture. Is the topog- raphy regular? Irregular? Flat in one area from a small Salzmann's nodule or scar or EBMD? Placido disc-based topographers are best in my hands for cataract purposes, where Scheimpflug are critical for corneal refractive." IOL power calculation and formulas Even with the best keratometers, measurements should be validated for IOL power calculations. "In general, IOL power calculations are best carried out using high-quality autokeratometry with the application of validation guidelines for the specific instrument being used," Dr. Hill said. Regarding the formulas used for these calculations, he recommends the Barrett and Hill-RBF formulas. Dr. Raviv agreed, noting "the published literature has demonstrated the superiority of the Barrett Universal II and Hill-RBF over all older formulas." 1,2 The Barrett formulas—with variants for post-LASIK/PRK/RK cases and for toric IOLs—were created by Graham Barrett, MD, and are available on the ASCRS website at ascrs.org/barrett-toric-calculator, among other websites. Meanwhile, the Hill-RBF Calculator is avail- able via rbfcalculator.com, where it is described as "an advanced, self-validating method for IOL power selection employing pattern recognition and sophisticated data interpolation." "The current version 2.0 is based on 12,419 implan- tations," Dr. Hill said. "This works for biconvex and meniscus IOLs from +32.00 D down to –5.00 D. "As the database increases in size, the depth and accuracy of the Hill-RBF method will advance," he added. "Version 3.0, which will be T oday, surgeons are able to achieve desired refractive outcomes with greater precision than ever before. EyeWorld corresponded with three experts on how to best utilize biom- etry and astigmatism management to achieve emmetropia, improving patient satisfaction and ensuring surgeons' success in refractive cataract surgery. Biometry: Due for an upgrade? The right biometer can help better achieve desired refractive outcomes. "I think that the [two] key elements of state-of-the-art biometry are (1) optical measurement of axial length, by optical low-coherence reflectometry [OLCR] or preferably swept-source OCT, which has the advantage of being able to measure axial through much more dense cataracts than OLCR can, and (2) measurement of corneal curvature with at least 18 LEDs, preferably in more than one ring," said Douglas Koch, MD. "Lacking these, an upgrade will dramatically improve outcomes." The latest biometers have certainly im- proved keratometry readings, said Tal Ra- viv, MD, noting that "both the LENSTAR [Haag-Streit] and IOLMaster 700 [Carl Zeiss Meditec] take multiple simultaneous measure- ments on multiple points of the central and paracentral cornea to derive their K1 and K2." They also indicate whether the tear film is un- stable, requiring optimization—a critical factor for refractive outcomes. "If a surgeon is using an early generation optical biometry with old software, then moving to a newer biometer with the most recent IOL power selection methods would allow for better outcomes," said Warren Hill, MD. The technology, however, isn't without lim- itations. "No one should trust a single measure- ment, in my view," Dr. Koch said. "I can cite plenty of examples where my biometer gave incorrect readings, almost always due to inaccu- rate corneal measurements." As such, he recommended performing topography. "Topography is essential (1) to confirm the meridian and to a lesser extent the Precision refractive cataract surgery Biometry, astigmatism control, and enhancements At a glance • The latest biometry devices are essential but must be validated according to instrument-specific guidelines and are best paired with topography. • The use of multiple IOL calculation formulae is recommended; the Barrett and Hill-RBF are generally acknowledged as having the best results. • Astigmatism control can be achieved using relaxing incisions for lower, toric IOLs for higher levels of astigmatism. • Enhancements, whether by corneal procedures or IOL exchange, require additional skills or partnering with other surgeons but are an essential component of refractive cataract surgery.

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