Optical Incoherence Tomography: a method to generate tomographic retinal cross-sections with non-interferometric adaptive optics ophthalmoscopes

Abstract

We present Optical Incoherence Tomography (OIT): a completely digital method to generate tomographic retinal cross-sections from en-face through-focus image stacks acquired by non-interferometric imaging systems, such as en-face adaptive optics (AO)-ophthalmoscopes. We demonstrate that OIT can be applied to different imaging modalities using back-scattered light, including systems without inherent optical sectioning and, for the first time, multiply-scattered light, revealing a distinctive cross-sectional view of the retina. The axial dimension of OIT cross-sections is given in terms of focus position rather than optical path, as in OCT. We explore this property to guide focus position in cases where the user is "blind" focusing, allowing precise plane selection for en-face imaging of retinal pigment epithelium, the vascular plexuses and translucent retinal neurons, such as photoreceptor inner segments and retinal ganglion cells, using respectively autofluorescence, motion contrast and split detection techniques.

Adaptive-glasses time-domain FFOCT for wide-field high-resolution retinal imaging with increased SNR

“…However, a mismatch of the coherence gate and focal plane positions produces low SNR FFOCT images. At the full-aperture, e.g., for a 7 mm pupil diameter, the depth of focus is approximately 10 times thinner than the retina, making focus position an essential step [14]. During each imaging session, SD-OCT B-scans are displayed in real-time, allowing the user to select the retinal layer of interest, where the coherence gate is then automatically positioned.…”

“…One important hurdle of AO-OCT for clinical translation is the challenge of allying high-spatial resolution with a wide FOV, which is beneficial for clinical applications. The combination of FFOCT and the adaptive-glasses approach opens a new avenue to wide FOV high-resolution retinal imaging in a where photoreceptors were not resolved but were nevertheless automatically detected and discarded using the method proposed by [14]. The total time necessary to obtain such an image (including subject alignment, image acquisition, and processing) is about 15 min.…”

Spatial frequency-based image reconstruction to improve image contrast in multi-offset adaptive optics ophthalmoscopy

“…AO ophthalmoscopes were first used to detect back-scattered photons to image highly reflective retinal features, such as cones and nerve fiber layer. Later on, by displacing laterally the detection position compared to the illumination, the use of multiply scattered photons was made possible, increasing contrast of translucent retinal structures not previously visualized [4–10]. Different implementations of such off-axis detection methods on both AO-SLO and AO-FIO, as offset aperture, split detection, dark-field, and multi-offset contributed to directly image red blood cells, blood vessel walls, photoreceptor inner segment and ganglion cells in-vivo .…”

Partial-Field Illumination Ophthalmoscope: improving the contrast of a camera-based retinal imager

“…Taking it one step further, the partial-field illumination ophthalmoscope could spread across an even larger range of imaging techniques. One straightforward application is the use of the partial-field illumination ophthalmoscope approach to carry out dark-field imaging on a camera-based retinal imager [17][18][19][20]. Indeed, by setting the pixels corresponding to illuminated regions to zero, instead of non-illuminated regions, dark-field images could be obtained in a post-processing manner.…”