Eyeworld

44 | EYEWORLD | FALL 2024 R EFRACTIVE by Ellen Stodola Editorial Co-Director About the physicians David Huang, MD, PhD Wold Family Endowed Chair in Ophthalmic Imaging Professor of Ophthalmology and Biomedical Engineering Casey Eye Institute Oregon Health & Science University Portland, Oregon Dan Reinstein, MD, MA(Cantab) London Vision Clinic EuroEyes Group London, U.K. George Waring IV, MD Waring Vision Institute Mt. Pleasant, South Carolina E pithelial mapping has rapidly gained attention over the last decade with the advent of high-resolution diagnostic devices, specifically high-resolution OCT and ultrasound biomicroscopy (UBM), each of which offer unique advantages. OCT, said George Waring IV, MD, is more readily available commercially and more effi- cient in the clinic and provides ease of use for both staff and patients. Ultrasound is less sus- ceptible to optical artifacts, which has additional advantages in terms of reliability of scans and less optical noise. The normative data has been well described at this point, he said, as well as epithelial mapping software that's been validat- ed for both types of diagnostics. "We've participated in the early research in epithelial mapping with high-resolution OCT, and this was a big part of our early studies for crosslinking," Dr. Waring said, adding that it also helped with understanding the natural history of keratometric normalization after ep- ithelial removal in an irregular stromal surface curvature. Dr. Waring mentioned the early research on understanding the role of epithelial mapping in myopic LASIK and the variation in central thick- ness epithelial maps that correlate with higher ablation profiles and their potential impact on residual refractive error. 1,2 Dr. Waring also men- tioned David Huang, MD, PhD, inventor of OCT, and his thesis on being able to discern contact lens warpage and ectasia through epithelial mapping software with a high degree of sen- sitivity and specificity, and said Dan Reinstein, MD, should be credited for the development of high-resolution ultrasound and application of it for corneal- and lens-based refractive surgery. Dr. Reinstein has done extensive research 3–13 on the topic. With all of these advancements and devel- opments, Dr. Waring said the jury is still out on the universal application of epithelial mapping and its understanding relating to residual refractive error. As it relates to predicting and adjusting for variation in epithelial thickness in refractive enhancements, Dr. Waring said this can apply to post-LASIK patients, or any corneal refractive procedure patient, where the corneal curvature has been changed. There is a lot of interest in being able to better predict refractive outcomes in the post-corneal refractive state where the epithe- lium is non-uniform, Dr. Waring said. Multiple attempts have been made to try to predict re- fractive outcomes in the setting of non-uniform epithelium, and uses for this would be in the post-myopic or post-hyperopic LASIK patient who is interested in an enhancement or the post-myopic LASIK patient who had an IOL now with residual refractive error. "If we were to unmask the non-uniform epithelium, that may have some variation and decrease predictability in our refractive planning as we've decoupled the masking of the non-uniform epithelium in a way we can't entirely correlate with refraction and therefore the correction of residual refractive error," Dr. Waring said. "Our opinion is that, although we routinely perform epithelial mapping and study it, we keep this in mind in our planning and in setting expectations with our patients and documenting these expectations about the unpredictability." Dr. Waring doesn't think there is enough data to support the refractive adjustments in planning based on epithelial mapping alone. "We think that there could be a role for fur- ther predictive analysis perhaps with artificial intelligence and finite element modeling on the refractive implications," he said. "However, this is a dynamic circumstance where the epithelium is going to attempt to normalize the corneal curvature irrespective of the prediction." Dr. Huang said epithelial mapping can be helpful for the post-cataract surgery patient who might have a good refractive outcome and have residual myopia, hyperopia, or astigma- tism. "I think in that situation, before you do any corrective procedure, you want to make sure the cornea has stabilized in terms of edema by following the pachymetric map and in terms of epithelial remodeling by following the epi- thelial thickness map." The shape of the cornea can often change slightly because of the corneal incision; the epithelium will adjust to that, and that takes a while to settle down. Dr. Huang said that an epithelial map can show that dry eye will often have an uneven Epithelial mapping: applications for residual refractive error and current technology continued on page 46

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