Abstract
Purpose :
Phase-contrast adaptive optics scanning light ophthalmoscopy (AOSLO) enhances the visibility of translucent cells in the living retina. A model by Guevara-Torres suggests that the contrast is generated by the steering of light as it passes through refractive retinal cells that act as microscopic lenses. Here, we show for the first time, evidence that light is indeed bent by single retinal cells and laterally shifted at deeper retinal layers. This measurement provides information for detection optimization. Aperture patterns that favorably collect such steered light, can increase the contrast of translucent cells in the retina.
Methods :
A digital micromirror device (DMD) was placed in the detection plane of a mouse AOSLO to image the light distribution in the retina. 796 nm light (241uW) was focused in the outer nuclear layer, while the detection plane was positioned conjugate to the deeper photoreceptor (PR)/RPE complex. The light distribution at the detector plane was imaged by turning on/off DMD facets to create a “flying” pinhole (~4.3 Airy disc diameter). A gradient descent algorithm optimized the aperture pattern by maximizing retinal image contrast (Brenner gradient, BG). Aperture pattern was trained on in vivo data from 3 adult C57BL/6J mice and was tested on a 4th mouse.
Results :
The light distribution was laterally shifted at deeper layers by as much as 6 µm consistent with a positive lens, showing that single translucent cells can lens and steer light (Fig.1). With the light distribution imaged, we could optimize the image contrast with an aperture pattern that highlights the lateral differences induced by cell steering. Starting from a random pattern, our algorithm iterated the aperture patterns to enhance the image contrast, which converged in 10 iterations (Fig. 2). Optimizing the BG in the horizontal direction, the trained aperture converged to an asymmetric pattern that resembled a split detector aperture that matched the differential light distribution seen by cell steering.
Conclusions :
This strategy shows the first images of the directional steering of light by single retinal cells as light propagates to deeper retinal layers. We find that by optimizing the aperture this distribution of light can provide a further contrast improvement with the ultimate goal of providing intrinsic contrast for translucent cells in the retina.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.