REFRACTIVE 32 EWAP MARCH 2023 to be the “father” of this new diagnostic field of layered corneal diagnostics. “Having developed and worked with VHF digital ultrasound for 20 years prior, I was excited to help Optovue develop the first OCT prototype device to map the corneal epithelium in 2012, which commercially launched in 2015. Most anterior segment 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 epithelial 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 produced 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 physicians find epithelial mapping helpful in keratoconus detection. 5 Prof. Reinstein told EyeWorld that while the Insight 100 VHF digital ultrasound (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 keratoconus 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 formula 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 corneal 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 surgery candidacy, but there are still A patient who presented for corneal refractive surgery was found to have inferior steepening on topography. Epithelial mapping revealed epithelial hyperplasia, suggesting that the course of inferior steepening was related to an epithelial irregularity rather than early keratoconus. Source: Jessica Heckman, OD, and Ralph Chu, MD
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