Time-domain full-field optical coherence tomography (TD-FF-OCT) in ophthalmic imaging

Cellular structural and functional imaging of donor and pathological corneas with label-free dual-mode full-field optical coherence tomography

In this study, a dual-mode full-field optical coherence tomography (FFOCT) was customized for label-free static and dynamic imaging of corneal tissues, including donor grafts and pathological specimens. Static images effectively depict relatively stable structures such as stroma, scar, and nerve fibers, while dynamic images highlight cells with active intracellular metabolism, specifically for corneal epithelial cells. The dual-mode images complementarily demonstrate the 3D microstructural features of the cornea and limbus. Dual-modal imaging reveals morphological and functional changes in corneal epithelial cells without labeling, indicating cellular apoptosis, swelling, deformation, dynamic signal alterations, and distinctive features of inflammatory cells in keratoconus and corneal leukoplakia. These findings propose dual-mode FFOCT as a promising technique for cellular-level cornea and limbus imaging.

Optical tomography in a single camera frame using fringe-encoded deep-learning full-field OCT

Optical coherence tomography is a valuable tool for in vivo examination thanks to its superior combination of axial resolution, field-of-view and working distance. OCT images are reconstructed from several phases that are obtained by modulation/multiplexing of light wavelength or optical path. This paper shows that only one phase (and one camera frame) is sufficient for en face tomography. The idea is to encode a high-frequency fringe patterns into the selected layer of the sample using low-coherence interferometry. These patterns can then be efficiently extracted with a high-pass filter enhanced via deep learning networks to create the tomographic full-field OCT view. This brings 10-fold improvement in imaging speed, considerably reducing the phase errors and incoherent light artifacts related to in vivo movements. Moreover, this work opens a path for low-cost tomography with slow consumer cameras. Optically, the device resembles the conventional time-domain full-field OCT without incurring additional costs or a field-of-view/resolution reduction. The approach is validated by imaging in vivo cornea in human subjects. Open-source and easy-to-follow codes for data generation/training/inference with U-Net/Pix2Pix networks are provided to be used in a variety of image-to-image translation tasks.

Optical Coherence Tomography (OCT): A Brief Look at the Uses and Technological Evolution of Ophthalmology

Medical imaging is the mainstay of clinical diagnosis and management. Optical coherence tomography (OCT) is a non-invasive imaging technology that has revolutionized the field of ophthalmology. Since its introduction, OCT has undergone significant improvements in image quality, speed, and resolution, making it an essential diagnostic tool for various ocular pathologies. OCT has not only improved the diagnosis and management of ocular diseases but has also found applications in other fields of medicine. In this manuscript, we provide a brief overview of the history of OCT, its current uses and diagnostic capabilities to assess the posterior segment of the eye, and the evolution of this technology from time-domain (TD) to spectral-domain (SD) and swept-source (SS). This brief review will also discuss the limitations, advantages, disadvantages, and future perspectives of this technology in the field of ophthalmology.

Physical compensation method for dispersion of multiple materials in swept source optical coherence tomography

An ophthalmic swept source-optical coherence tomography (SS-OCT) system based on a high-speed scanning laser at 1060 nm with a scanning rate of 100 KHz is constructed. Since the sample arm of the interferometer is comprised of multiple glass materials, the ensuing dispersion severely degrades imaging quality. In this article, second-order dispersion simulation analysis for various materials was performed first, and dispersion equilibrium was implemented utilizing physical compensation methods. After dispersion compensation, an imaging depth in air of 4.013 mm was achieved in model eye experiments, and signal-to-noise ratio was enhanced by 11.6%, with a value of 53.8 dB. In vivo imaging of the human retina was performed to demonstrate structurally distinguishable retinal images, characterized by an axial resolution improvement of 19.8%, with a value of 7.7 μm close to the theoretical value of 7.5 μm. The proposed physical dispersion compensation method enhances imaging performance in SS-OCT systems, enabling visualization of several low scattering mediums.

Non-invasive in vivo imaging of human corneal microstructures with optical coherence microscopy

Non-invasive imaging systems with cellular-level resolution offer the opportunity to identify biomarkers of the early stage of corneal diseases, enabling early intervention, monitoring of disease progression, and evaluating treatment efficacy. In this study, a non-contact polarization-dependent optical coherence microscope (POCM) was developed to enable non-invasive in vivo imaging of human corneal microstructures. The system integrated quarter-wave plates into the sample and reference arms of the interferometer to enable deeper penetration of light in tissues as well as mitigate the strong specular reflection from the corneal surface. A common-path approach was adopted to enable control over the polarization in a free space configuration, thus alleviating the need for a broadband polarization-maintained fiber. The POCM achieved volumetric imaging of corneal microstructures, including endothelial cells over a field of view 0.5 × 0.5 mm2 with an almost isotropic resolution of ∼2.2 µm and a volume (500 × 500 × 2048 voxels) rate of 1 Hz. A self-interference approach between the corneal surface and underlying layers was also developed to lessen the corneal curvature and axial motion artifacts, thus enabling high-resolution imaging of microstructures in the anterior cornea, including squamous epithelial cells, wing epithelial cells, basal epithelial cells, sub-basal nerve plexus, and stromal keratocytes.