EyeWorld India March 2015 Issue

IOL Calculations March 2015 26 EWAP SECONDARY FEATURE Barrett Toric Calculator aims for accurate outcomes by Vanessa Caceres EyeWorld Contributing Writer 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; president of the Australasian Society of Cataract & Refractive Surgeons; and president of the Asia-Pacific Association of Cataract and Refractive Surgeons (APACRS). He began work on the calculator by reflecting on improving cataract surgery outcomes. “Of all the things that have happened 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 improvement for patients is modest or debatable,” he said. “With a toric lens, it’s quite Barrett Toric Calculator Source: Graham Barrett, MD AT A GLANCE • Graham Barrett, MD, recently devised the Barrett Toric Calculator for toric IOL calculation. • 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. different. You really change what you can do for the patient. “ However, using a toric lens requires 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 four 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 four concepts put the Barrett Toric Calculator in context, Dr. Barrett said. About the calculator Surgeons may feel bewildered by the sheer number of toric IOL calculators available, Dr. Barrett said. He said that his is unique because it takes into account the posterior cornea and considers lens position for each individual patient versus using what is known about the average eye. Dr. Barrett’s calculator uses the Universal II formula, which he also devised. The formula considers 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 astigmatism 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