In-vivo Three-dimensional Characteristics of Bowman’s Layer and Endothelium/Descemet’s Complex Using Corneal Microlayer Tomography in Healthy Subjects

ABSTRACT

Purpose: To characterize the three-dimensional (3D) thickness profile and age-related changes of Bowman’s layer (BL), and endothelium/Descemet’s membrane (En/DM) complex among healthy individuals using Corneal Microlayer Tomography (CML-T), and to describe its repeatability and accuracy.

Methods: Sixty-six eyes of 41 healthy volunteers; 27 eyes (< 40 years old), and 39 eyes (>40 years old) were imaged using HD-OCT. Automatic and manual segmentation of the corneal layers was performed, and 3D thickness maps were generated, using custom-built CML-T software. A regional analysis of mean thickness parameters between the 2 age groups was performed. A regression analysis was used to assess the correlation between age, and thickness maps. Intraclass Correlation Coefficients (ICC), Coefficients of Variation (COV), and Bland-Altman plots were used to assess the reliability of the repeated measurements in 198 locations.

Results: CML-T successfully mapped the BL and En/DM in all included eyes. Thickness maps showed a significant increase in corneal thickness (CT), BL thickness (BMT), and En/DM complex thickness (DMT) toward the periphery with a mean difference 28 µm (p < .001), 1.1 µm (p < .001), and 1.4 µm (p < .001), respectively. There was a strong correlation between age and central DMT (r = 0.61; p < .001), while there was no correlation between age and both CT, and BMT. ICC values ranged from 0.9 (BMT) to 0.997 (DMT), and from 0.808 (BMT) to 0.979 (CT) for intraoperator repeatability of manual measurements, and the accuracy of auto matic measurements, respectively. COV values were lower than 7.5% in all cases.

Conclusion: CML-T is a novel tool that can generate 3D-thickness maps of both BL and En/DM. CT, BMT, and DMT increase toward the periphery in healthy corneas. DMT increases with aging, while BMT does not. We also report excellent repeatability, accuracy and good agreement between automatic and manual measurements.

KEYWORDS:

• Optical coherence tomography
• Bowman’s layer
• descemet’s membrane
• corneal endothelium
• thickness maps

Ethics approval and consent to participate

This study was approved by the University of Miami Institutional Review Board.

Availability of data and material

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Conflicts of interest

Taher K. Eleiwa, Amr Elsawy, Zeba A Syed, Vatookarn Roongpoovapatr and Ahmed M. Sayed - None to declare. Sonia H. Yoo and Mohamed Abou Shousha: United States Non-Provisional Patents (Application No. 8992023 and 61809518), and PCT/US2018/013409. Patents and PCT are owned by University of Miami and licensed to Resolve Ophthalmics, LLC. Mohamed Abou Shousha and Sonia Yoo are equity holders and sit on the Board of Directors for Resolve Ophthalmics, LLC. Sonia H. Yoo is a consultant of CARL Zeiss.

Authors’ contributions

All authors analyzed and interpreted patients’ data, contributed in writing the manuscript and approved the final manuscript.

Abbreviations

BCVA: best-corrected visual acuity

OCT: optical coherence tomography

AS-OCT: anterior segment optical coherence tomography

UHR-OCT: ultra-high resolution optical coherence tomography

(PS)-OCT: polarization sensitive optical coherence tomography

TD-OCT: time domain optical coherence tomography

SD-OCT: spectral domain optical coherence tomography

FD-OCT: Fourier-domain optical coherence tomography

CML-T: corneal microlayers tomography

BL: Bowman’s layer

En/DM: Endothelium-Descemet’s complex

CT: Corneal thickness

BMT: Bowman’s layer thickness

DMT: Descemet-Endothelium complex thickness

ANOVA: analysis of variance

3D: three-dimensional

2D: two-dimensional

SD: standard deviation

LASIK: laser-assisted in-situ keratomileusis

KC: keratoconus

BEI-MAX: maximum Bowman’s layer ectasia index

EEI-MAX: maximum epithelium ectasia index

RANSAC: Random sample consensus

ICC: intraclass correlation coefficients

COV: coefficient of variance

Additional information

Funding

This study was supported by NEI K23 award K23EY026118 (MAS), NEI core center grant to the University of Miami [P30 EY014801], and unrestricted grant from Research to Prevent Blindness, NY. The funding organizations had no role in the design or conduct of this research.