Müller cell alignment in bird fovea: possible role in vision.

Birds which possess high visual acuity, such as eagles and falcons, are known to have retinas with a deep conically curved central foveal pit. There have been different attempts to explain the importance of this particular shape of the fovea in visual resolution. Recently, the function of Müller cells as "light fibers" was discovered, showing how the endfeet of Müller cells trap the light and then transfer it to a single cone photoreceptor. Here we describe how the endfeet of Müller cells line the walls of the foveal pit in the Pied Flycatcher, and how the Müller cell body extends its processes towards individual cones, forming machinery that could allow for light transfer from the pit wall to the photoreceptor layer alongside the pit. We describe how this construction may send an image from the fovea to the cones, and also, how the angular positioning of Müller cells, being optical extensions of the cones, has the advantage of being much denser than on a flat or slightly curved fovea. We, therefore, suggest that this type of optic fiber alignment can be used as a novel type of "amplifying array" that simply increases the amount of megapixels at the photoreceptor cell layer.