Eyeworld

EW FEATURE 66 IOL calculations February 2015 by Vanessa Caceres EyeWorld Contributing Writer "Of all the things that have hap- pened over the last 10 to 15 years in cataract surgery, many of them make you wonder about the huge amount of money spent when the improve- ment for patients is modest or debat- able," he said. "With a toric lens, it's New formula considers lens position, posterior corneal curvature I n the quest for better surgical outcomes for toric IOLs, Graham Barrett, MD, has created the Barrett Toric Calculator. Dr. Barrett is a consultant ophthalmic surgeon at Sir Charles Gairdner Hospital, Nedlands, Western Australia; pres- ident of the Australasian Society of Cataract & Refractive Surgeons; and president of the Asia-Pacific Association of Cataract & Refractive Surgeons (APACRS). His work on the calculator began as part of a reflec- tion on improving cataract surgery outcomes. Barrett Toric Calculator aims for accurate outcomes quite different. You really change what you can do for the patient. " However, using a toric lens re- quires more legwork for the surgeon than a conventional IOL. "It's more demanding than a non-toric lens. If you want to get the best outcomes, you have to think about 4 things: 1) the device used to measure the cornea, 2) interpreting those measurements, 3) a measurement of prediction that's accurate, and 4) when you have the right method, you need something to let you put the lens on the right axis," he said. Those 4 concepts put the Barrett Toric Calculator in context. About the calculator Surgeons may feel bewildered by the sheer number of toric IOL calcula- tors available, Dr. Barrett said. He said that his is unique because it takes into account the posterior cor- nea and considers lens position for each individual patient versus using what is known about the average eye. "My formula uses the Universal II, which is a method of predicting IOL power to work out where the AT A GLANCE • Graham Barrett, MD, recently devised the Barrett Toric Calculator for toric IOL calculations. • The formula takes into consideration lens position and posterior corneal curvature without actually measuring curvature. • The calculator was more accurate compared with other formulas in studies that will be published soon. • The calculator is available on the ASCRS and APACRS websites. There's an app for that: toriCAM A nother recent addition to Dr. Barrett's work is a free app he created for iPhones and iPads called the toriCAM. It provides a way to determine axis of the corneal limbal marks used as a reference to find the correct alignment for a toric IOL during surgery, according to the app description. It can also measure the axis of an implanted IOL at the slit lamp postop. "If you have an accurate reference axis, then your markings are perfect," Dr. Barrett said. "The app is a free and simple method to make sure once you have a calculator with precise measurements." To see an in-depth interview with Dr. Barrett on the app, visit ewreplay.org, search for "Graham Barrett toriCam" or select "ESCRS" from the "Video Archives" dropdown menu, then select "2014" and "Sunday." Dr. Barrett is featured in the first video that day discussing the app and giving a demonstration of its use. EW Barrett Toric Calculator Source: Graham Barrett, MD lens is and uses that to calculate what is the effect of the cylinder power at the cornea," he said. Dr. Barrett also devised the Universal II formula. Dr. Barrett's formula consid- ers the thickness and shape of the lens as well, which provides a more sophisticated way of predicting and translating the cylinder power, he said. The formula is able to predict posterior corneal curvature without actually measuring it. "The reason it can do so is I looked at all the observations that people have made, especially Doug Koch [MD, Houston], about the posterior cornea," he said. It has long been known that the posterior cornea tends to have a half diopter of against-the-rule effect on the astig- matism of the eye, he said. Although that has been known since the late 1800s, it has not been accounted for in other toric lens calculations, Dr. Barrett said. "The reality is, if you have against-the-rule astigmatism, it's aligned in the vertical meridian. I

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