Corneal Total and Epithelial Thickness Measured by Sonogage Ultrasound Pachometry and High-resolution Optical Coherence Tomography

Abstract

SIGNIFICANCE This research questions the validity of using the Sonogage ultrasound (US) pachometer to measure corneal epithelial thickness and coincidentally provides confirmation for the conventional view of the mechanism of orthokeratology (OK) based on central epithelial thinning. PURPOSE The Sonogage (Corneo-Gage Plus 1) pachometer uses A-scan US to measure total corneal thickness. It is claimed that this instrument can also measure corneal epithelial thickness. We sought to validate this claim by comparing total and epithelial thickness measurements with the Sonogage with those obtained with high-resolution optical coherence tomography (OCT). METHODS Fourteen non–contact lens wearers and 14 subjects who had worn Paragon CRT OK lenses overnight for greater than 1 month were recruited. Three OCT and five US measurements were taken in one eye of each subject. Depending on normality of data, paired t tests or Wilcoxon tests were used to compare total and epithelial thicknesses measured with the Sonogage pachometer and the Tomey Casia OCT. Pearson or Spearman correlation analyses were used to examine relationships between measurements obtained with the two instruments. RESULTS There was a significant difference in total corneal thickness measurements between the two instruments. Although a significant correlation was found (r = 0.916, P < .001), the Sonogage consistently measured greater total corneal thickness than did the OCT (+19.5 ± 9.2 μm; P < .001). Epithelial thickness using the Sonogage showed little variation (range, 46.4 to 50.0 μm), whereas epithelial thickness using the OCT ranged from 30.7 to 54.7 μm. There was no significant correlation between epithelial thicknesses obtained with the two instruments (r = −0.135, P = .49). Epithelial thickness measured by OCT was significantly thinner in OK wearers (35.8 ± 2.8 μm) than in nonlens wearers (46.7 ± 4.5 μm, P < .001). CONCLUSIONS The Sonogage is not able to measure epithelial thickness in vivo, returning essentially identical measurements over a range of epithelial thicknesses. Optical coherence tomography measurements confirm the conventional view of the mechanism of OK based on central epithelial thinning.

Post-Ortho-K Corneal Epithelium Changes in Myopic Eyes

“…Wang et al found thinning of the central epithelium and thickening in the midperiphery [ 18 ]. Several other studies have also found central corneal epithelial thinning [ 5 – 7 , 19 , 20 ] and flattening, with corneal curvature and myopia reduced and unaided visual acuity at 20/20 or better. In contrast with these findings, the present study found that thinning of the paracentral epithelium and thickening in the midperiphery happened at temporal half-meridian.…”

“…There is a lack of consensus to date on corneal epithelium redistribution after ortho-K lenses wear. Swarbrick et al [ 7 ] found that the epithelium measured using OCT was significantly thinner in ortho-K wearers than in nonlens wearers, not evolving paracentral and peripheral corneal epithelium. Interventions to control myopia take effect over time, so it is important to understand corneal changes that occur in prolonged ortho-K lens wear.…”

The Biomechanical Response of the Cornea in Orthokeratology

“…The mesh and boundary conditions are shown in Figure 2 . Clinical studies have proven that principally only the thickness of the corneal epithelium and the curvature of the anterior cornea are changed when wearing an ortho-k lens, without bending of the entire cornea or affecting the depth of the anterior chamber ( Alharbi and Swarbrick, 2003 ; Kim et al, 2018 ; Swarbrick et al, 2020 ). Therefore, in our model, the sclera was constrained from moving in all directions.…”

Effect of Lid-Wiper Epitheliopathy on the Corneal Epithelial Thickness Distribution: A Novel Semiautomatic Quantitative Method

“…Lid wiper epitheliopathy (LWE) is de ned as damage to the epithelium of the lid wiper, primarily caused by insu cient lubrication of the ocular surface for various reasons (such as inadequate interface lubrication, uneven corneoconjunctival surface, abnormal blinking pattern, and frequency), leading to increased friction between the lid wiper and the ocular surface [8][9][10] . This indicates that LWE may be a potential factor contributing to the uneven distribution of CET, and this aspect has been consistently overlooked in previous studies [11][12][13] .…”