Three-dimensional (3D) cellular-resolution imaging of the living human retina over a large field of view would bring a great impact in clinical ophthalmology, potentially finding new biomarkers for early diagnosis and improving the pathophysiological understanding of ocular diseases. While hardware-based and computational Adaptive Optics (AO) Optical Coherence Tomography (OCT) have been developed to achieve cellular-resolution retinal imaging, these approaches support limited 3D imaging fields and their high cost, and their intrinsic hardware complexity limit their practical utility. Here, we demonstrate 3D depth-invariant cellular-resolution imaging of the living human retina over a 3-mm × 3-mm field of view using the intrinsically phase-stable multi-MHz retinal swept-source OCT and tailored computational defocus and aberration correction methods. Single-acquisition imaging of photoreceptor cells, retinal nerve fiber layer, and retinal capillaries is presented across unprecedented imaging fields. By providing wide-field 3D cellular-resolution imaging in the human retina using a standard point-scan architecture routinely used in the clinic, this platform proposes a strategy for expanded utilization of high-resolution retinal imaging in both research and clinical settings.
The study of choroidal blood flow is severely limited by the deficiencies of existing flow imaging methods. We introduce a new framework and acquisition protocol for optical coherence tomography (OCT) flowmetry in the choroid. Our approach quantifies choroidal flow by applying a robust mathematical analysis to signals that are dynamically forward scattered (DFS) by choroidal vessels and reflected from static scatterers in the sclera. This DFS approach provides robust and quantitative flow measurements that are immune to angle and gradient artifacts. We further demonstrate a visualization of flow mapping in a healthy human eye.
KEYWORDS: Optical coherence tomography, Retina, Imaging systems, Chromium, Range imaging, Ophthalmology, Human subjects, Frequency combs, Computing systems, System integration
Intraoperative OCT can markedly enhance visualization in both posterior and anterior eye procedures. In these applications, imaging speed is paramount, as slower systems interfere with surgical workflow. We have previously introduced a circular-ranging (CR) OCT architecture optimized for high-speed intraoperative applications. Here, we demonstrate retinal imaging by CR-OCT for the first time. We achieved a 13.5 MHz A-line rate and performed high-quality wide-field and video-rate normal-field imaging in human subjects. The compressive properties of CR allow each of these imaging modes to operate with reduced data capture, easing acquisition and processing requirements that are critical to achieving continuous and low-latency imaging.
Scanning laser ophthalmoscopy is a confocal imaging technique that allows high-contrast imaging of retinal structures. Rapid, involuntary eye movements during image acquisition are known to cause artefacts and high-speed imaging of the retina is crucial to avoid them. To reach higher imaging speeds we propose to illuminate the retina with multiple parallel lines simultaneously within the whole field of view (FOV) instead of a single focused line that is raster-scanned. These multiple line patterns were generated with a digital micro-mirror device (DMD) and by shifting the line pattern, the whole FOV is scanned. The back-scattered light from the retinal layers is collected via a beam-splitter and imaged onto an area camera. After every pattern from the sequence is projected, the final image is generated by combining these back-reflected illumination patterns. Image processing is used to remove the background and out-of-focus light. Acquired pattern images are stacked, pixels sorted according to intensity and finally bottom layer of the stack is subtracted from the top layer to produce confocal image. The obtained confocal images are rich in structure, showing the small blood vessels around the macular avascular zone and the bow tie of Henle's fiber layer in the fovea. In the optic nerve head images the large arteries/veins, optic cup rim and cup itself are visualized. Images have good contrast and lateral resolution with a 10°×10° FOV. The initial results are promising for the development of high-speed retinal imaging using spatial light modulators such as the DMD.
A method is proposed for determining blood oxygen saturation in frozen tissue. The method is based on a spectral
camera system equipped with an Acoustic-Optical-Tuneable-Filter. The HSI-setup is validated by measuring series of
unfrozen and frozen samples of a hemoglobin-solution, a hemoglobin-intralipid mixture and whole blood with varying
oxygen saturation. The theoretically predicted linear relation between oxygen saturation and absorbance was observed in
both the frozen sample series and the unfrozen series. In a final proof of principal, frozen myocardial tissue was
measured. Higher saturation values were recorded for ventricle and atria tissue compared to the septum and connective
tissue. These results are not validated by measurements with another method. The formation of methemoglobin during
freezing and the presence of myoglobin in the tissue turned out to be possible sources of error.
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