Despite the recent development of advanced ophthalmic imaging techniques, volumetric fluorescence angiography (vFA) over a large field of view is still lacking. Fundus photography techniques have significant limitations due to the lack of 3D imaging capability. Scanning laser ophthalmoscopy (SLO) and confocal SLO (cSLO) use confocal gating to remove diffused light, resulting in crisper image quality. However, the volumetric imaging of SLO requires to compile z stacks, which can be challenging and time-consuming. Adaptive optics SLO (AOSLO) allows diffraction-limited resolution in both axial and lateral resolution. This technique is limited however, by its small field of view (FOV) and also the necessity of z stacks for volumetric imaging. To fill the technical void of vFA over a large field of view (FOV), we developed a novel retinal imaging modality called oblique scanning laser ophthalmoscopy (oSLO) for in vivo volumetric fluorescence retinal imaging. By using oblique illumination and detection, oSLO essentially allows “OCT-like” cross-sectional images contributed solely by the fluorescent contrast, without the need for z stacking. We will demonstrate 3D vFA over a 30˚x30˚ FOV in vivo in mouse retina. We will further report a high-speed oSLO in imaging capillary hemodynamics. The new capability allows the calculation of capillary hematocrit and blood speed in 3D, which can be potentially valuable in diabetic retinopathy and macular degeneration.
Elastic light scattering spectroscopy (ELSS) has been proven as a powerful tool in characterizing tissue native structures with superb sensitivity. As a widely used technique, optical coherence tomography (OCT) would have been well suited for ELSS measurement by using a broadband light source. However, OCT-based ELSS is largely hampered by the limited k-space spectral bandwidth from all existing OCT systems. To overcome this barrier, we report a simple all fiber-based setup to implement dual-channel visible and near infrared (NIR) optical coherence tomography (vnOCT) for human retinal imaging, bridging over 300nm spectral gap. Remarkably, we discovered a newly available fiber that supports single-mode propagation and maintains high interference efficiency for both visible and NIR light with fringe visibility of 97% and 90%, respectively, which was previously considered impossible to use the same fiber components for such a broad range of wavelengths. Longitudinal chromatic aberration from the eye is corrected by a custom-designed achromatizing lens. As retinal imaging being an important OCT application, we demonstrated vnOCT on human retina and further developed robust ELSS analysis method to quantify spectroscopic contrast in several import layers of human retina. This vnOCT platform and method of ELSS analysis open new opportunities in understanding structure-function relationship in the human retina and in exploring new biomarkers for retinal diseases.
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