Wide field volumetric fluorescence retinal imaging by oblique scanning laser ophthalmoscopy (oSLO)

While fluorescence imaging is widely used in ophthalmology, three-dimensional (3D) fluorescence retinal imaging over large field of view (FOV) has never been reported up to date. In this paper, for the first time, we describe a novel oblique scanning laser ophthalmoscopy (oSLO) technique that provides wide-field 3D volumetric fluorescence retinal imaging. The technique utilizes scanned oblique illumination and an angled detection to obtain fluorescent cross-sectional images analogous to the OCT line scans (or B-scans). By breaking the coaxial optical alignment used in conventional retinal imaging modalities, depth resolution is drastically improved. To demonstrate the capability of oSLO, we have performed in vivo volumetric fluorescein angiography (FA) of the rat retina with ~25μm depth resolution and over 30˚ field of view. Using depth segmentation, oSLO can obtain high contrast images of the microvasculature down to single capillaries in 3D. The multi-modal nature of oSLO also allows for seamless combination with simultaneous OCTA. We believe that the volumetric imaging capability in oSLO can potentially revolutionize the current clinical practice of fluorescence retinal imaging, by better detection of vessel leakage and intrinsic autofluorescence (AF) markers in 3D.