Epithelial, Stromal, and Total Corneal Thickness in Keratoconus: Three-dimensional Display With Artemis Very-high Frequency Digital Ultrasound

Abstract

PURPOSE To characterize the epithelial, stromal, and total corneal thickness profile in a population of eyes with keratoconus. METHODS Epithelial, stromal, and total corneal thickness profiles were measured in vivo by Artemis very high-frequency (VHF) digital ultrasound scanning (ArcScan) across the central 6- to 10-mm diameter of the cornea on 54 keratoconic eyes. Maps of the average, standard deviation, minimum, maximum, and range of epithelial, stromal, and total corneal thickness were plotted. The average location of the thinnest epithelium, stroma, and total cornea were found. The cross-sectional semi-meridional stromal and total corneal thickness profiles were calculated using annular averaging. The absolute stromal and total corneal thickness progressions relative to the thinnest point were calculated using annular averaging as well as for 8 semi-meridians individually. RESULTS The mean corneal vertex epithelial, stromal, and total corneal thicknesses were 45.7 ± 5.9 µm, 426.4 ± 38.5 µm and 472.2 ± 41.4 µm respectively. The average epithelial thickness profile showed an epithelial doughnut pattern characterized by localized central thinning surrounded by an annulus of thick epithelium. The thinnest epithelium, stroma, and total cornea were displaced on average by 0.48 ± 0.66 mm temporally and 0.32 ± 0.67 mm inferiorly, 0.31 ± 0.45 mm temporally and 0.54 ± 0.37 mm inferiorly, and 0.31 ± 0.43 mm temporally and 0.50 ± 0.35 mm inferiorly, respectively, with reference to the corneal vertex. The increase in semi-meridional absolute stromal and total corneal thickness progressions was greatest inferiorly and lowest temporally. CONCLUSIONS Three-dimensional thickness mapping of the epithelial, stromal, and total corneal thickness profiles characterized thickness changes associated with keratoconus and may help in early diagnosis of keratoconus.

Screening for Ectasia Risk: What Are We Screening For and How Should We Screen For It?

“…Additional metrics, especially epithelial thickness mapping with very high frequency ultrasound 25,26 or high-resolution optical coherence tomography, 27,28 can differentiate keratoconic and normal eyes and seem promising for detecting early corneal ectatic processes. Other hopeful but as yet unvalidated techniques include biomechanical characterization using the Ocular Response Analyzer (Reichert, Buffalo, NY), which, although theoretically promising, 10 has demonstrated limited ability in screening for ectatic diseases, 29,30 and the recently FDA-approved Oculus Corvis ST. 31 Ambrósio & Randleman/Editorial SUMMARY: SCREENING TODAY So, what should we be using to screen our patients in 2013?…”

Corneal Physiology and Responses to Cross-Linking and Intracorneal Rings in Keratoconus

“…13 The difference between the thinnest and thickest epithelium showed a stronger correlation with the steepest keratometry than the thinnest epithelium or thickest epithelium alone. 9 the basal cells. If damaged, fibronectin levels increase and the process of healing can take up to 6 weeks.…”

“…Total corneal thickness changes associated with keratoconus are due to changes in both stromal thickness and epithelial thickness. 9 The corneal epithelium has the ability to alter its thickness profile to re-establish a smooth, symmetrical optical surface and either partially or totally mask the presence of an irregular stromal surface from front surface corneal topography. In keratoconus, the epithelium is known to be thin in the area overlying the cone, and in advanced keratoconus, there may be excessive epithelial thinning leading to a breakdown in the epithelium.…”

Anterior Eye Imaging with Optical Coherence Tomography

“…In diseases such as keratoconus, the thickness of the epithelium becomes altered to reduce corneal surface irregularity [46]. Therefore, the presence of an irregular stroma may be less measurable by frontal surface corneal topography.…”

“…Accurate and reproducible measurement of corneal epithelial thickness provides important information for assessing corneal remodeling after refractive surgeries such as photorefractive keratectomy and LASIK [45]. Moreover, deviations from normal epithelial thickness could be an early sign of keratoconus [46].…”