High-resolution wide-field OCT imaging of anterior corneal layers using a near-normal incidence scanning beam.

Abstract

Purpose : Prior studies suggest that keratoconus affects the epithelium and Bowman’s layer from the center to the periphery of the cornea, offering potential for early keratoconus detection. Conventional OCT systems face challenges in imaging the periphery of these corneal layers due to signal and resolution losses caused by corneal steepness. This study aims to develop an OCT system capable of high-resolution imaging and thickness measurements of anterior corneal layers from the center to the periphery of the cornea.

Methods : We developed an SD-OCT system operating at a central wavelength of 840 nm and with an axial resolution of 4 µm (in air). The OCT delivery system consists of a dual mirror scanner and a custom-made multielement scanning lens that focuses the OCT beam nearly perpendicular to the corneal surface. The optical design of the lens was optimized to provide a lateral field of 11mm, an OCT beam diameter from 30 to 35 µm (1/e²) from the center to the periphery of the field, near-normal incident ray angles with the cornea (< 8 degrees), and minimal optical path difference between incident rays over the full field. The OCT signal is detected by a commercially available spectrometer (Envisu 2300, Leica microsystems) which provides an imaging depth of 3.4 mm and imaging rate of 32,000 Alines/sec. Preliminary imaging tests were performed on the right eye of a 28-year-old subject with no history of corneal diseases. Epithelium and Bowman’s layer thickness (mean ± std) was calculated over a 1mm region at the center and the nasal periphery of the cornea.

Results : The figure shows an OCT image of the cornea acquired with the system. The image is distorted due to the scanning architecture. Epithelium (Epi) and Bowman’s layer (BL) are visible from the center to the periphery of the cornea (11mm). The basal cells layer of the epithelium (BE) is displayed as a hypo-reflective layer across the entire cornea. Epithelium thickness was 53.1 ± 0.8 μm centrally and 55.1 ± 0.6 μm at the cornea periphery. Bowman’s layer showed a thickness of 17.9 ± 0.6 μm at the center and 17.5 ± 0.1 μm at the periphery of the cornea.

Conclusions : The study demonstrates the capability of the system to image and quantify the thickness of the anterior corneal layers with high resolution from the center to the periphery of the cornea. The system holds potential as a diagnostic tool for early Keratoconus detection.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.