We demonstrate the feasibility of a multimodal AO flood-illumination ophthalmoscope, able to provide both bright-field and dark-field images. The multimodality was made possible by integrating a digital micromirror device (DMD) at the illumination path to project a sequence of complementary high-resolution patterns into the retina. Owing to the given system, and the proposed acquisition/processing pipeline, we were able, at the same time, to: (1) obtain up to four-fold contrast improvement in bright-field modality when imaging highly scattered structures such as PRs and NFL; and (2) to visualize, through phase contrast images, translucent retinal features such as capillaries, red blood cells, vessel walls, ganglion cells, and PRs inner segment.
Adaptive optics imaging techniques are invaluable for cellular-level retina visualization. While AO Flood illumination ophthalmoscopes provide distortion-free, high-speed images, they lack contrast. On the other hand, AO scanning laser ophthalmoscopes offer highly contrasted images due to point by point illumination and spatial filtering but suffer from low pixel throughput and distortion artifacts. Our recent advancements, using a DMD integrated AO-FIO, show that we can illuminate and capture multiple spatially separated zones, achieving contrast close to the one of a confocal microscope. Our theoretical framework emphasizes that each zone must be smaller than 100μm in both directions or smaller than 10μm in only one direction to minimize the diffuse light component. Building upon these results, we developed a cutting-edge confocal rolling slit ophthalmoscope, able to achieve brightfield contrast similar to a confocal ophthalmoscope, along with phase contrast images. We utilize a classical sCMOS camera with a rolling shutter synchronized with the line source scanning of the field of view. The system makes use of all the incident photons that can be collected, whether singly, multiply scattered or absorbed. Easy digital switching between the darkfield and brightfield, as well as modification of the size and offset of the detection aperture, enhances the adaptability and versatility of this multimodal imaging system, allowing for fine-tuning of imaging modalities and comprehensive exploration of the retina.
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