Science Literature

Glial cells have been known to neuroscientists for over a century and they perform numerous essential functions. Now we can add another. In the vertebrate eye, there are "radial glial cells spanning the entire retinal thickness" known as Muller cells. Shaped like an extended funnel, they are "oriented along the direction of light propagation". These cells "provide a low-scattering passage for light from the retinal surface to the photoreceptor cells", thus acting as optical fibres. Their function is to "mediate the image transfer through the vertebrate retina with minimal distortion and low loss".

For years, we have been told by "blind watchmaker" Darwinians that the eye is an example of bad design because light has to pass through the retina to reach the photoreceptor cells. These folk insist that a good Designer wouldn't have wired our retinas the "wrong" way. The response from those who advocate design has been to show that the eye is an example of optimum design: there are good reasons that can be advanced for having an inverted retina. This approach has satisfied many but certainly not all. The "bad design" claim is still widespread.

This new paper has finally nailed the argument: by revealing yet another level of exquisite design. The authors modestly say: "This finding elucidates a fundamental feature of the inverted retina as an optical system". They describe the Muller cells as "ingeniously designed light collectors". ScienceNow says: "For an organ that delivers such crystal-clear images, the eye is curiously designed. Its light-sensing rods and cones lie hidden behind a blanket of nerve cells that carry visual information to the brain. So what prevents those neurons from obscuring our vision? The answer may be surprisingly high-tech." So, in addition to optimal design arguments, we can now appreciate how these distinctive cells address completely the main perception of compromised design. One of the authors is quoted as saying: "Nature is so clever". Surely, it has to be myopic not to discern here the hallmarks of an intelligent designer. This is argument from evidence par excellence!

Muller cells are living optical fibers in the vertebrate retina
Kristian Franze, Jens Grosche, Serguei N. Skatchkov, Stefan Schinkinger, Christian Foja, Detlev Schild, Ortrud Uckermann, Kort Travis, Andreas Reichenbach, and Jochen Guck.
Proceedings of the National Academy of Sciences USA, May 15, 2007, vol. 104, no. 20, 8287-8292. | 10.1073/pnas.0611180104

Abstract: Although biological cells are mostly transparent, they are phase objects that differ in shape and refractive index. Any image that is projected through layers of randomly oriented cells will normally be distorted by refraction, reflection, and scattering. Counterintuitively, the retina of the vertebrate eye is inverted with respect to its optical function and light must pass through several tissue layers before reaching the light-detecting photoreceptor cells. Here we report on the specific optical properties of glial cells present in the retina, which might contribute to optimize this apparently unfavorable situation. We investigated intact retinal tissue and individual Muller cells, which are radial glial cells spanning the entire retinal thickness. Muller cells have an extended funnel shape, a higher refractive index than their surrounding tissue, and are oriented along the direction of light propagation. Transmission and reflection confocal microscopy of retinal tissue in vitro and in vivo showed that these cells provide a low-scattering passage for light from the retinal surface to the photoreceptor cells. Using a modified dual-beam laser trap we could also demonstrate that individual Muller cells act as optical fibers. Furthermore, their parallel array in the retina is reminiscent of fiberoptic plates used for low-distortion image transfer. Thus, Muller cells seem to mediate the image transfer through the vertebrate retina with minimal distortion and low loss. This finding elucidates a fundamental feature of the inverted retina as an optical system and ascribes a new function to glial cells.

See also:

Living fibre optics light up our eyes (Science Museum, 4 May 2007)

Sherriff, L. Living optical fibres found in the eye, The Register, Tuesday 1st May 2007

Ayoub, G. On the Design of the Vertebrate Retina, Origins & Design 17:1

Denton, M., The Inverted Retina: Maladaption or Pre Adaption? Origins & Design 19:2, Winter, 1999