Light Propagation through the Retina: Vertebrate Retinal Optics

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It is an old enigma how the vertebrate retina can function properly despite being inverted: light must pass all (light scattering) retinal layers before it can be detected by the photoreceptor cells. Recently we have shown that Müller radial glial cells act as light guiding fibers, bypassing the inner retinal layers. However, this light guidance must end at the outer nuclear layer where the Müller cell processes split into thin cytoplasmic tongues. Our collaborating partner has forwarded the hypothesis that the radial rows of photoreceptor cell nuclei serve as ‘chains of lenses’ bridging the distance between the Müller cell stem processes and the photoreceptor inner segments. To test this hypothesis and to elucidate the complex light path through the entire retina, we will perform (i) a quantitative analysis of the numerical relation between the subsequent light-guiding elements, (ii) a structural analysis of the ‘transition zone(s)’ between them, and (iii) a direct visualization of light transfer through the retina. For the latter purpose, laser light will be applied by a thin fiber to the inner surface of the retina. The light path of the laser beam will be monitored, as well as the fluorescence induced by it within the structures of the retina, labeled by fluorescent vital dyes. In collaboration with the partner in Cambridge, mathematical modeling of light transport through the retina will be performed.