Eyeworld

I THERAPEUTIC REFRACTIVE CORNEAL SURGERY N FOCUS 78 | EYEWORLD | APRIL 2020 E pithelial thickness mapping is known for its ability to help detect corneal disease, including keratoconus. Howev- er, it also can assist with treatment and enhancement decisions for LASIK and PRK, according to ophthalmologists who are using it. "I think we're just learning how to use this powerful technology," said Lance Kugler, MD. "It has taught me how critical the epithelium is to our visual system. The ability to measure it gives us a valuable tool for our treatment decisions." Dr. Kugler uses epithelial mapping with the Avanti OCT system (Optovue) with every new patient consultation, be it for LASIK, PRK, or even cataract surgery. After refractive surgery, Dr. Kugler and staff will obtain mapping and also do so on a case-by-case basis with IOL patients. This helps them to track progression of the maps over time. "Understanding the epithelial distribu- tion can improve clinical decisions, ranging from time of LASIK or PRK enhancement to selecting transepithelial PRK to epithelial debridement in eyes with map dot fingerprint dystrophy," said Kerry Assil, MD. His work with epithelial mapping with the SPECTRALIS OCT (Heidelberg Engineering) adapted for the anterior segment analyzes epithelial thickness, patterns, and remodeling over time. What's considered abnormal When reviewing epithelial maps, ophthalmol- ogists using them must keep in mind what's outside of the norm. "A normal epithelial thickness is 50 µm, but what OCT gives us is a pattern and an overview of thickness over a larger area of the cornea," said Y. Ralph Chu, MD. "This pattern can help determine areas of relative thinner or thicker epithelium, which can be helpful in detecting abnormal curvatures of the cornea." Abnormalities that Dr. Assil considers in- clude unusually hypertrophic central epithelium, variably irregular distribution, and insufficient Using epithelial mapping for LASIK, PRK, and refractive enhancement by Vanessa Caceres Contributing Writer At a glance • Epithelial thickness mapping has a role in guiding treatment and enhancement decisions related to LASIK and PRK. It also helps with patient education. • Mapping can help surgeons decide what sort of treatment may be used post-refractive surgery, even several years later. • Understanding of the use of epithelial mapping with refractive surgery patients will continue to grow. About the doctors Kerry Assil, MD Medical director The Assil Eye Institute Beverly Hills, California Y. Ralph Chu, MD Founder and medical director Chu Vision Institute Bloomington, Minnesota Lance Kugler, MD Assistant professor Truhlsen Eye Institute University of Nebraska Medical Center Omaha, Nebraska buffering of prior scars. The latter may include apical epithelial hypoplasia coupled with sur- rounding hypertrophy, he said. Something additional that Dr. Kugler con- siders is the bilaterality of the results. "The two eyes should look the same. If you have 60 µm in one eye and 30 in the other, you know one eye is not normal. Fifty microns is the norm, but some people are thicker or thinner," he said. Guiding treatment 10 years later Ophthalmologists interviewed by EyeWorld con- sidered how they would handle a patient who was 10 years post-LASIK and had a normal epi- thelial thickness. Based on what they saw with epithelial thickness mapping, would they treat with flap relifting and laser or use PRK? "Since the advent of the femtosecond laser, eyes 10 years post-LASIK are no longer amenable to routine flap relifting, due to firm adherence," Dr. Assil said. "While nearly all post-myopic PRK and LASIK eyes demon- strate some degree of epithelial hypertrophy, the observation of an unusually large degree of hypertrophy might make a relift more appeal- ing." This can help avoid "reshuffling the deck," as Dr. Assil described it. Both PRK and flap relifting are reasonable, Dr. Kugler thinks. If choosing PRK, make sure to consider how much epithelial thickness there is. "If it doesn't grow back to the same thickness, you'll have some residual refractive error. Be cognizant of that, and realize it may take longer than you think to get to the original thickness," he said. Dr. Chu prefers PRK and removing the ep- ithelium for that procedure. "I know there are some cases where epithelial hyperplasia results in some slight myopic regression, and a simple debridement can help resolve the small refrac- tive error," he said. He knows of other sur- geons who have used an excimer laser to treat the epithelium to remove hyperplasia, although he has not performed that himself.

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