How light traverses the inverted vertebrate retina

Abstract

In our eyes, as in the eyes of all vertebrates, images of the environment are projected onto an inverted retina, where photons must pass through most of the retinal layers before being captured by the light-sensitive cells. Light scattering in these retinal layers must decrease the signal-to-noise ratio of the images and thus interfere with clear vision. Surprisingly however, our eyes display splendid visual abilities. This apparent contradiction could be resolved if intraretinal light scattering were to be minimized by built-in optical elements that facilitate light transmission through the tissue. Indeed, we were able to show that one function of radial glial (Muller) cells is to act as effective optical fibers in the living retina, bypassing the light-scattering structures in front of the light-sensitive cells. Each Muller cell serves as a ‘private’ light cable, providing one individual cone photoreceptor cell with its appropriate pixel of the environmental image, thus optimizing special resolution and visual acuity.