It is well known that the mammalian eye has an “inverted” structure, whereby light reaching the retinal surface must pass through a layer of cellular tissue before reaching the light-sensitive cells: the rods and cones. The cellular tissue can be expected to degrade the clarity of vision, and this has been interpreted by some as convincing evidence that the eye has not been designed intelligently, but has been cobbled together by processes characterized by chance and contingency. Responses have majored on the concept of optimization: the inverted structure provides benefits that compensate for any disadvantages. Most evolutionary biologists appear to be unconvinced, and the issue of eye design has become an icon of evolution: proof that intelligent agency was absent in whatever process formed the mammalian eye. In 2010, an editorial in New Scientist expressed it this way:
“[Evolutionists] say that the “inside out” vertebrate retina – curiously structured so that its wiring obscures the light sensors and leaves us with a blind spot – can be described as one of evolution’s “greatest mistakes”. The anatomy of the retina is indeed good evidence that eyes were cobbled together bit by bit. Surely a creator would never have chosen to construct an eye in this way. In return, creationists have argued that the backwards retina clearly has no problems providing vertebrates with excellent vision – and even that its structure enhances vision.” (Source here)
We should note that the editorial fails to recognise that design advocates used evidence-based reasoning to make the case for optimal design. Nevertheless, all previous contributions to the eye design issue need to be updated by the discovery of Muller cells in retinal tissue, first reported in 2007 and then in 2010 (here and here), and which immediately put “bad design” advocates on the defensive.
The latest findings about these cells (published July 2014), elucidate their role as optical fibres that carry light from the retinal surface to the cone photoreceptors. Most of the incoming light is guided onto the cones (thereby sensing colour), but some of the blue light is leaked into the surrounding tissue and is sensed by the rods. This optimizes daytime and nighttime vision and any lingering thoughts that the retinal tissue has a negative impact on vision are effectively refuted. John Hewitt provides a physicist’s perspective when he writes:
“A case in point are the Muller glia cells that span the thickness of the retina. These high refractive index cells spread an absorptive canopy across the retinal surface and then shepherd photons through a low-scattering cytoplasm to separate receivers, much like coins through a change sorting machine. A new paper in Nature Communications describes how these wavelength-dependent wave-guides can shuttle green-red light to cones while passing the blue-purples to adjacent rods.” (Source here)
The researchers have found the eye to be even more complex and structured than was previously known. The eye really is an model system for understanding optimal design! There are good reasons for having retinal tissues in front of the photoreceptors, but any negative impacts of having this structure are removed by the use of optical fibre cells. Here is John Hewitt again:
“Having the photoreceptors at the back of the retina is not a design constraint, it is a design feature. The idea that the vertebrate eye, like a traditional front-illuminated camera, might have been improved somehow if it had only been able to orient its wiring behind the photoreceptor layer, like a cephalopod, is folly.” (Source here)
Comments like this are a challenge to die-hard evolutionists who appear never to be able to learn from their mistakes. As a case in point, consider the reaction of one biologist quoted in the New Scientist editorial of 2010:
“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.”
Contrast this with Hewitt’s affirmation that the “inverted” eye structure is a “design feature”, not a “design constraint”. The retrofit hypothesis is a deduction from Darwinian dogma, and should not be presented as a scientific statement. What we can say positively is that the optimal design arguments developed in the past by ID and creationist scientists are unaffected, and the new research vindicates the design perspective. The “bad design” arguments are devoid of substance.
Muller cells separate between wavelengths to improve day vision with minimal effect upon night vision
Amichai M. Labin, Shadi K. Safuri, Erez N. Ribak and Ido Perlman
Nature Communications, 8 July 2014, 5, Article number: 4319 | doi: 10.1038/ncomms5319
Abstract: Vision starts with the absorption of light by the retinal photoreceptors—cones and rods. However, due to the ‘inverted’ structure of the retina, the incident light must propagate through reflecting and scattering cellular layers before reaching the photoreceptors. It has been recently suggested that Müller cells function as optical fibres in the retina, transferring light illuminating the retinal surface onto the cone photoreceptors. Here we show that Müller cells are wavelength-dependent wave-guides, concentrating the green-red part of the visible spectrum onto cones and allowing the blue-purple part to leak onto nearby rods. This phenomenon is observed in the isolated retina and explained by a computational model, for the guinea pig and the human parafoveal retina. Therefore, light propagation by Müller cells through the retina can be considered as an integral part of the first step in the visual process, increasing photon absorption by cones while minimally affecting rod-mediated vision.
See also:
Confirmation of a Creationist Prediction Becomes Even More Stunning, by Jay L. Wile (Proslogion, August 11, 2014)