A low-cost, easy-to-implement optical add-on to convert a retinal OCT into a ultra-high-resolution corneal OCT

Commercial anterior segment optical coherence tomography (OCT) systems typically offer sufficient axial resolution to distinguish corneal layers. However, their lateral resolution (∼15-20 µm) is limited, restricting the visualization of fine microstructural features, relevant for noninvasive diagnosis of corneal pathologies. We present a low-cost, easy-to-implement optical add-on that substantially improves the lateral resolution of a standard retinal OCT system, enabling high-fidelity corneal imaging.

Custom-designed optical modules were developed for the standard objective lens of an investigational retinal OCT device. The system design, incorporating a single achromatic lens, was optimized through optical simulations to achieve a higher numerical aperture and reduced focal length. The lateral resolution was evaluated both theoretically, via point spread function, and experimentally using a 1951 United States Air Force (USAF) resolution target. A compact prototype, presented here, was tested on a commercial SPECTRALIS OCT2, compared with the commercial Anterior Segment Module (both Heidelberg Engineering GmbH, Heidelberg, Germany), and tested in vivo on two human subjects, including one with suspected epithelial basement membrane dystrophy (EBMD).

The prototype achieved a lateral resolution of 3.1µm in the experiment, closely matching the results of the optical simulation. This resolution is markedly better than the 15.6µm achieved with the commercial corneal OCT, albeit at a cost of a reduced field of view (2.62mm vs. 8.29mm). In vivo imaging confirmed enhanced visualization of epithelial microstructures in both healthy and pathological corneas, despite a reduced depth of focus resulting from the higher numerical aperture.

The proposed add-on enabled ultra-high-resolution corneal imaging on a standard SPECTRALIS OCT2 platform without the need for major hardware modifications, such as an increased reference arm or dispersion compensation. This low-cost, easy-to-implement approach offers diagnostic value for early detection and longitudinal monitoring of subtle corneal irregularities, particularly in conditions such as EBMD, where a high lateral resolution is critical for clinical decision-making.