CORNEA 28 EWAP DECEMBER 2022 Miller said. “The problem with those devices is they only see a small portion of the anterior surface of the cornea; they don’t see the total cornea. You have to make assumptions about the back surface of the cornea if you’re only measuring the anterior surface of the cornea. You can use the Barrett formula for that, for instance.” Dr. Miller noted that some, like Warren Hill, MD, have put forth the idea that the posterior surface measurements might not be all that accurate and measuring the anterior surface and making assumptions might produce an equally adequate result. Dr. Miller said he doesn’t share this perspective but some physicians do. 6. Look for LASIK and PRK. Dr. Miller said that 10 –15% of his cataract practice includes patients who have had prior PRK or LASIK. “On any given day, there is a good chance that I am operating on someone who has had prior laser vision correction surgery,” he said. The catch is some of them don’t include these procedures in their medical history. Even if you ask them if they’ve had prior eye surgery, many say no. Dr. Miller said they don’t necessarily consider LASIK to be “eye surgery.” Topography, tomography, or OCT “will save you from doing surgery on people you didn’t know had refractive surgery,” he said. “You think you should be able to see this prior surgery when you examine them, but you can’t see PRK, and in some eyes it is difficult to see LASIK. The edge of the LASIK flap is just so well healed, it looks normal,” he said. A biometry measurement is unlikely to reveal prior refractive surgery, Dr. Miller said, unless the cornea is significantly flatter than you think it should be, but even that is nuanced with lower treatments. 7. Onboarding new equipment. When you bring in a new imaging modality, Dr. Miller said to take time to evaluate it against the imaging you were using before. “I will continue doing the old thing, image them with the new thing, and retrospectively look at if I chose to go with the old thing, will the new thing give me a better outcome?” he said. “I think every time we bring in new equipment, you need to evaluate it in some way and … not just suddenly flip over to the new and abandon what you were doing before and maybe getting good results with.” ‘Garbage in, garbage out’ Every instrument has its own quirks, and you’ve got to pay attention to various factors to get a quality image and measurement for IOL selection, Dr. Miller said. “There is a famous computer saying: Garbage in, garbage out. If you have a person not looking in the right direction, their eyes are dry, their head is tilted 30 degrees, guess what? You’re going to get terrible information by which to operate on,” he said Lens power formulas are looking for inputs, values, Dr. Miller continued. There are many possible inputs, but the most important ones are corneal curvature and axial length. Of these, he said axial length is the most important to nail, with small errors in measurement resulting in large errors in lens power. Biometers do a good job of this, Dr. Miller said. For corneal power, Dr. Miller said most ophthalmologists still use biometers, but he thinks Scheimpflug and OCT devices that look at the front and back surface of the cornea are best for calculating a toric lens. “I think measuring corneal power with these devices and planning out your astigmatism management is better than using a simple biometer,” he said. EWAP Editors’ note: Dr. Koch practices at Department of Ophthalmology, Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and has interests with Alcon, Bausch + Lomb, Carl Zeiss Meditec, and Johnson & Johnson Vision. Dr. Miller is Kolokotrones Chair in Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, and has interests with Alcon and Oculus. The ablation in this tomography map is slightly decentered. Decentered ablations can almost never be seen on slit lamp biomicroscopy. Regular corneal astigmatism can be observed in the central portion of the map. Source (all): Kevin M. Miller, MD
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