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EW NEWS & OPINION 10 March 2017 The analyzer helps determine the amount of IOL rotation and the expected residual refraction. Barrett toric IOL calculator This calculator for toric IOLs takes into account the posterior cornea and considers lens position for each individual patient versus using what is known about the average eye. Its formula uses the Universal II, which is a method of predicting IOL power to work out where the lens is and uses that to calculate the effect of the cylinder power at the cornea. Dr. Barrett also devised the Universal II formula. This formula considers the thickness and shape of the lens as well, which provides a more so- phisticated way of predicting and translating the cylinder power. The formula is able to predict posterior corneal curvature without actually measuring it. Post-refractive IOL calculator The post-refractive surgery IOL power calculator was the first tool added to the website in 2006. It can be used to estimate the IOL power following multiple forms of kera- torefractive surgery. The most recent addition has been the Barrett True K method, which is available for myopic and hyperopic LASIK/PRK and prior radi- al keratotomy. In February, the Bar- rett True K method for prior radial keratotomy was updated to include pre- and post-operative refractive data for enhanced outcomes. As many of these patients have experi- enced consecutive hyperopia, even if only the current refraction is known, entering this information improves the calculation accuracy. EW Editors' note: Dr. Hill has financial interests with Haag-Streit. Dr. Barrett has no financial interests related to his comments. Contact information Barrett: graham.barrett@uwa.edu.au Hill: hill@doctor-hill.com surgically induced astigmatism (SIA) also is considered by the tool when it calculates an IOL exchange or piggyback IOL. However, SIAs are not considered when rotating a toric lens. Warren Hill, MD, Mesa, Ari- zona, noted that the new tool goes beyond the toric measurement abil- ity of the most popular, currently available tool, which addresses only the optimal meridian of alignment. "When evaluating a refractive surprise for the toric IOL, the Barrett Rx formula provides a unique, three- part solution: the optimal meridian of alignment, a manufacturer-spe- cific toric power, and any change necessary to the spherical power to obtain the required refractive objec- tive," Dr. Hill said. Hill-RBF calculator Among the other IOL power calcu- lation tools available on the ASCRS website is the Hill-RBF Calculator, which is an advanced, self-validat- ing method for IOL power selection employing pattern recognition based in artificial intelligence. That calculator—added to the website in 2016—was optimized for use with biometry data from the Lenstar LS 900 (Haag-Streit, Köniz, Switzerland) optical biom- eter and may also be used with data from other optical biometers, which provide clinically equivalent biometry data as the Lenstar LS 900. It will work with a wide variety of biconvex IOLs in the power range of +30.00 D to +6.00 D. The Hill-RBF calculator is the product of a worldwide collabora- tive effort involving 26 surgeons in 14 countries and updates will be at regular intervals. Additional information can be found at rbfcalculator.com/index. html#popup1. The next update will include a greatly expanded boundary model and the addition of meniscus design IOLs with a power range down to –5.00 D. Toric results analyzer The Toric Results Analyzer was developed by John Berdahl, MD, Vance Thompson Vision, Sioux Falls, South Dakota, and David Hardten, MD, Minnesota Eye Consultants, Minnetonka, Minnesota, to help de- termine if a previously placed toric IOL is ideally aligned. By comparing the current location of the toric IOL to a patient's current manifest refrac- tion, the Toric Results Analyzer can determine if rotating the toric IOL would decrease residual astigmatism. Optical continued from page 3 For eyes with near normal pre-operative measurements, most modern IOL power selection methods are expected to give good outcomes. The popular Wang-Koch axial length modification for older formulas is an excellent way to extend their accuracy range in the setting of high to extreme axial myopia. For short eyes, all formulas tend to be less accurate and the differences between them for a series of patients is surprisingly small. For eyes with unusual anterior segments, the more advanced formulas are typically required to achieve acceptable outcomes. Source: Warren Hill, MD

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