Eyeworld

60 | EYEWORLD | DECEMBER 2022 R EFRACTIVE OCT manufacturers are now developing this capability for their devices," Prof. Reinstein said. "This is becoming the standard of care for refractive surgery diagnostics." […] According to Prof. Reinstein's work, the average central epithelial thickness in a normal cornea was 53.4 µm with a standard deviation of 4.6 µm, 3 measured by the gold standard method, Artemis 60 MHz 3D VHF digital ultrasound. "This indicated that there was little variation in central epithelial thickness in the population," he said. "The thinnest epi- thelial point within the central 5 mm of the cornea was displaced on average 0.33 mm (±1.08) temporally and 0.90 mm (±0.96) superiorly with reference to the corneal vertex. Studies using OCT have confirmed this superior-inferior and nasal-temporal asymmetric profile for epithelial thickness in normal eyes." 3 Prof. Reinstein first postulated in 1994 that this inferior/superior asymmetry is pro- duced by the balance of forces of epithelial outward growth and the combined inward forces produced by the eyelids, the upper eyelid producing more inward force than the lower lid, he explained. 4 As in the March 2021 article, many physi- cians find epithelial mapping helpful in kerato- conus detection. 5 Prof. Reinstein told EyeWorld that while the Insight 100 VHF digital ultra- sound (VHFDU) is the "gold standard" because it measures the epithelium alone without the tear film, which can vary in thickness between blinks, it takes more time. Therefore, he said he uses OCT epithelial mapping for keratoco- nus screening routinely for all patients. From there, he said about 10% of suspects will go on to receive an Insight 100 epithelial thickness map to further rule out keratoconus and inform their options for corneal refractive surgery. Prof. Reinstein added that obtaining anterior segment scans at the same time also means that the necessary measurements are available for optimal ICL sizing, if the patient is found not to be suitable for corneal surgery. "Sizing with VHFDU using our new formu- la 6 appears to have reduced ICL exchange rates to less than 1 in 200. This is available at www.iclsizing.com," Prof. Reinstein said. Dr. Trattler also sees the value in using epithelial mapping to rule out keratoconus for possible refractive surgery. Dr. Trattler said there are a lot of sophisticated technologies refractive surgeons are currently using to help assess candidates, including evaluating corne- al shape, thickness maps of the entire cornea, relative thickness maps, corneal biomechanics, scoring systems, etc. "We use a lot of information provided by these technologies to determine refractive sur- gery candidacy, but there are still patients who are borderline. Is it truly keratoconus or not?" he said, explaining that what might look like keratoconus could in fact be epithelial hyperpla- sia, the latter of which wouldn't rule out corneal refractive surgery. While epithelial mapping is not critical for a practice in Dr. Trattler's mind, he said it is quicker than waiting to assess for possible kera- toconus progression 6 months to a year later. "This provides a rapid way of understand- ing what's going on now versus monitoring patients over time," he said. Arjan Hura, MD, also does not think that epithelial mapping is standard of care yet, but he took an informal survey of refractive sur- geons and found that of 88 respondents, 60% routinely use it. He personally will get an epi- thelial map for patients with borderline or irreg- ular topography and when planning enhance- ments. For the latter, it helps him ascertain what degree of the postoperative refractive shift may be due to zonal epithelial hyperplasia. "I keep in mind that ocular surface disease, recent instillation of topical drops, and contact lens wear can impact the appearance of the epithelial maps. I don't make decisions based solely off epithelial mapping, and the amount of significance I give it varies by case," Dr. Hura said. "Overall, I view epithelial mapping as a valuable additional data point that has potential to help the surgeon in clinical decision making." Dr. Hura explained that he finds epithelial mapping most helpful in the context of to- pography. He offered these examples: (1) An area of topographic steepening with overlying corresponding epithelial thinning would be potentially concerning for keratoconus or ecta- sia. However, if the epithelium in that area of steepening is thick, it may be that the epithe- lium is what is causing the steepening and not References 1. Reinstein DZ, et al. High-fre- quency ultrasound measure- ment of the thickness of the corneal epithelium. Refract Corneal Surg. 1993;9:385–387. 2. Reinstein DZ, et al. Arc-scan- ning very high-frequency digital ultrasound for 3D pachymetric mapping of the corneal epithe- lium and stroma in laser in situ keratomileusis. J Refract Surg. 2000;16:414–430. 3. Reinstein DZ, et al. Epithelial thickness in the normal cornea: three-dimensional display with Artemis very high-frequency digital ultrasound. J Refract Surg. 2008;24:571–581. 4. Reinstein DZ, et al. Corneal pachymetric topography. Oph- thalmology. 1994;101:432–438. 5. Reinstein DZ, et al. Corneal epithelial thickness profile in the diagnosis of keratoconus. J Refract Surg. 2009;25:604–610. 6. Reinstein DZ, et al. New sizing parameters and model for predicting postoperative vault for the implantable collamer lens posterior chamber phakic intraocular lens. J Refract Surg. 2022;38:272–279. continued from page 59

• Blank Page
• Blank Page (1)