Eyeworld

72 | EYEWORLD | SPRING 2026 R EFRACTIVE Reference 1. Wilson SE, Klyce SD. Quan- titative descriptors of corneal topography. A clinical study. Arch Ophthalmol. 1991;109:349–353. membrane dystrophy, but Dr. Trattler mentioned irregularities can also be due to corneal scars, corneal haze, and/or keratoconus. "Irregular corneal astigmatism not caused by dry eye disease can take many forms and is most often related to trauma, surgical interven- tion, or pathology," Dr. Klyce and Dr. McDonald said. Another technological newcomer to detect- ing corneal irregularities is epithelial mapping. Receiving its first FDA approval less than a decade ago, Dr. Trattler said we've learned the epithelium isn't always uniform. "You can have something called epithelial hyperplasia, where the corneal shape looks like keratoconus, but it's not. It's actually the thick- ening of the epithelium that is the cause of the irregular shape," he said. Dr. Trattler said he doesn't perform epi- thelial mapping routinely, as there is a lot of variability. "It's not a perfect science yet because it can sometimes be difficult for the imaging technologies to differentiate between the tear film and the actual epithelium," he explained. modeled with the Zernike series are those that are correctable with spherocylindrical optics (including regular astigmatism)." Dr. Trattler said imaging technologies have become more sophisticated over time, making it easier to identify both regular and irregular astigmatism. It's important just to do the imaging, Dr. Trattler said. "There are still many doctors who don't perform topography prior to cataract surgery, for example. When a screening topogra- phy is performed, it's a non-covered service, so there's a cost to the practice," he said. However, missing irregular astigmatism prior to cataract surgery can be a significant source of postop dissatisfaction. "When we look at patients' topography prior to cataract surgery, there is a surprising number of patients who have irregular astigma- tism, and the topography reveals that," he said, adding later that treating irregular astigmatism is dependent on what's causing it. The most common causes of irregular astigmatism are dry eye and epithelial basement continued from page 70 Figure 2. These are the topographies of corneas of two patients after PRK. Mathematically convolving the Zernike polynomials with the Snellen eye chart shows excellent vision for OD even with a very large pupil. On the other hand, OS will have functional vision during the daytime with a small pupil but will experience distortion at night. Source: Stephen D. Klyce, PhD, FARVO, and Marguerite B. McDonald, MD, FACS

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