The eye is a funny thing. One interesting factoid is that the light sensitive rod and cone cells are actually buried within the retina, sandwiched between cells that give structure and perform the first parts of image formation. “If that’s the case,” you might ask, “how does light reach the photoreceptive cells?”

Research published in the May 15th issue of the Proceedings of the National Academy of Sciences, shows that Müller cells actually transport light through the retina. Basically they’re little optical fibers that guide light directly to rods and cones, increasing the eye’s efficiency and explaining the unusual location of the light-sensitive cells. (I learned about the paper via a summarizing article in July’s issue of Biophotonics International.)

Here’s an executive summary from PNAS:

An image focused by the lens on the front surface of the retina is conveyed by Müller cells to rods and cones on the retina’s rear face. Kristian Franze et al. observed that, when light is applied to the dissected retina of a guinea pig, a lattice of bright spots 2 µm in diameter and spaced 6 µm apart appears on the far side. The authors stained the retina with dyes and antibodies specific to Müller cells and confirmed that these long, funnel-shaped cells, which bridge the full thickness of the retina, are responsible for the light transmission. Held in a laser trap, Müller cells transmitted light efficiently across an optical gap. The cells’ refractive index is higher than that of surrounding tissue, and although their shape is not as regular as that of artificial optical fibers, they effectively function as such.