A previous blog drew attention to Glial (or Muller) cells that conduct light from the surface of the eye's retina to the photoreceptor cells. These cells provide a low-scattering passage for light from the retinal surface to the photoreceptor cells, thus acting as optical fibres. Their function was reported to "mediate the image transfer through the vertebrate retina with minimal distortion and low loss". New research in this area has increased knowledge of their functionality after constructing a light-guiding model of the retina outside the fovea. As a result, the "retina is revealed as an optimal structure designed for improving the sharpness of images".
Schematic of Muller cells funnelling light (source here)
These specialised cells do this in two ways: filtering out stray light and reducing colour dispersion. Stray light is a form of noise, so that the objects of interest are seen less clearly. It is found that the glial cells improve the signal-to-noise ration as light passes through them.
"The simulations showed that the Muller cells transmit a greater proportion of the former to the rods and cones below, while the latter tends to leak out. This suggests the cells act as light filters, keeping images clear. The researchers also found that light that had leaked out of one Muller cell was unlikely to be taken up by a neighbour, because the surrounding nerve cells help disperse it. What's more, the intrinsic optical properties of Muller cells seemed to be tuned to visible light, leaking wavelengths outside and on the edges of the visible spectrum to a greater extent."
The second mechanism relates to colour vision. "Just as light separates in a prism, the lenses in our eyes separate different colours, causing some frequencies to be out of focus at the retina". However, the glial cells have a diameter that is wider at the surface of the retina than at the cone photoreceptor at its base. The optical fibre structure of these cells brings significant improvements.
"Another notable result is that parafoveal color vision is less affected by chromatic aberrations. The longitudinal chromatic aberration spans the focal spot along the retina, where blue focuses before red. Thus both colors cannot be focused simultaneously on the cones. But with glial light guiding the configuration changes: Regardless of the volume of the focal spot, set by chromatic and monochromatic aberrations, the incidence angles are still within our analysis range of a few degrees. That means that they will still be guided by the same glial cell and lead to the same cone."
According to the report in New Scientist, these findings open up potentially fruitful areas for biomimetic research. "The new understanding of the role of Muller cells might find applications in more successful eye transplants and better camera designs, says Ribak." The human eye, which is already a remarkable example of functional engineering, continues to yield more evidences of exquisite design. All the more surprising, then, that Darwinians are persisting in their view that the eye should be listed among evolution's biggest "mistakes". An Editorial in New Scientist reaffirms the validity of this claim:
"Sure, sending light through Muller cells enhances vision, but that is not an argument for choosing to put the wiring in front of the sensors. It still creates a blind spot, where the nerves dive through the light-sensitive cells on their way to the brain. It would make much more sense to put Muller-like cells in front of the sensors, with the wiring behind. Rather than provide evidence in support of intelligent design, the new work is actually yet another example of evolution's extraordinary ability to create workaround solutions to problems arising from earlier iterations. Kenneth Miller, a biologist at Brown University in Providence, Rhode Island, and an untiring veteran of the creation-evolution wars, calls the Muller cells "a retrofit: a successful and highly functional adaptation made necessary by the original architecture of the retina, but a retrofit". The eye's structure, and the blind spot in particular, bears the unmistakable fingerprints of Darwinian evolution."
What we are seeing here fits what Thomas Kuhn called "normal science" in action. Darwinists never predicted the function performed by Muller cells, but once they were recognised, they are dubbed a "retrofit", with credit given to the amazing powers of mutation and natural selection (without any valid supporting evidence). This strategy is to Darwinism what epicycles were to the Ptolemaic cosmology. Actually, Kenneth Miller is retrofitting glial cells into the Darwinian model of the eye's evolution. He has to do this in order to save the theory in which so much intellectual capital is invested. But like the financial markets of today, crises will ensue. Just as commercial markets could not sustain high levels of debt indefinitely, so also Darwinism: they have borrowed excessively in order to sustain mutation and natural selection as viable mechanisms. When people look for substance, they find peppered moths and bird beaks. When they look carefuly, they find exquisite design - not tinkering evolution. All the Darwinists have left to defend their case is the blind spot - that is all that keeps them from the conclusion of optimal design.
Abstract: We construct a light-guiding model of the retina outside the fovea, in which an array of glial (Muller) cells permeates the depth of the retina down to the photoreceptors. Based on measured refractive indices, we propagate light to obtain a significant increase of the intensity at the photoreceptors. For pupils up to 6 mm width, the coupling between neighboring cells is only a few percent. Low cross talk over the whole visible spectrum also explains the insensitivity to chromatic aberrations of the eye. The retina is revealed as an optimal structure designed for improving the sharpness of images.
Editorial, The eye was evolution's great invention, New Scientist (6 May 2010)
McAlpine, K. Evolution gave flawed eye better vision, New Scientist (6 May 2010)
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