Eyeworld

68 | EYEWORLD | SEPTEMBER 2022 C ORNEA power for a lens, his primary imaging modality is a standard biometer (the Lenstar LS900 or IOLMaster). If he's doing astigmatism manage- ment, he also uses a topographer or tomogra- pher. He has a Galilei but said his workhorse instrument is the Pentacam AXL Wave (Oculus). Dr. Koch said, in general, if you're doing presbyopia-correcting IOLs, a tomography mea- surement should ideally be obtained to confirm a regular cornea that will provide the optical quality needed by the IOL. It also helps the surgeon know if a future enhancement could be possible. Considerations for quality images and analysis Dr. Miller said ophthalmologists are often reliant on technicians to ensure quality images and measurements are obtained. The surgeon then analyzes the data, seeing if it makes sense before using it in IOL planning. 1. Head positioning. "If the patient is too low or too high to the measurement axis or too far to the left or right, the topographer or to- mographer is going to be centering its measure- ments on a different part of the cornea rather than the actual center of the cornea. You want the patient to be perfectly centered," he said. Tilt of the patient's head should also be as- sessed. Even a 5- or 10-degree head tilt greatly affects measurement accuracy, Dr. Miller said. "Good technicians and good ophthalmol- ogists will make sure the patient is perfectly centered vertically and horizontally, and they will also make sure they are aligned and not tilted," he said. Even if the patient is positioned well on the X, Y, and Z axis, Dr. Miller said the tech needs to make sure they are looking in the right direc- tion. He said it's easy for patients to get distract- ed and look away, even if the instrument has a target for them to focus on. If patients are not looking at the target, Dr. Miller said it can result in measurements showing astigmatism or coma that does not exist. 2. Flag abnormalities and reimage, if necessary. Surface abnormalities (especially dry eye), contact lenses, cosmetic material, or de- bris in the tear film can "trip up measurements," Dr. Miller said. If the measurements or imaging appears off, Dr. Miller said that the hope is that you will notice before the patient goes home so they can be reassessed. "I obtain all the imaging before they see me. If I see issues, I can send them back before they leave," he said. continued from page 67 This Pentacam AXL Wave tomography map is from a patient who underwent LASIK years earlier. The central cornea has been flattened about 8.5 D. One part of the ablation zone is flatter than the rest, indicating irregular astigmatism. This would be a poor candidate for a multifocal IOL, even if the lens power calculation was perfect.

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