A friend must have been a really jumpin’ social event recently. Was buttonholed by a Darwin follower, just up from the crypt, who launched into the hoary old claim that the backwards eye wiring of vertebrates shows that the vertebrate eye is poorly designed—therefore not designed at all.
Now, of course, it is a non-sequitur to say that something that is poorly designed is not designed at all. Which is the followers’ point. Thus, it is unclear why they find eye wiring even an interesting argument, let alone a compelling one. No matter.
In any actual (rather than imaginary) situation, one can hope only for optimal, not “perfect” design. Perfection does not exist in time and space as we know it.
Dear God, the Uncommon Descent News team gives thanks to you today on behalf of our American friends, celebrating Thanksgiving. We especially praise you for the fact that the people who think that the vertebrate eye is poorly designed did not go into the kitchen and bathroom remodelling business. We beg you, in your infinite mercy, to keep things that way! Amen
The retina of the eye is the screen on which the eye’s optical image is focused. Nerves (bundled in the optic nerve) convey the image information to the brain. One would think the nerves (neurons) should come off the back of the retina, the side opposite the one having the image. But in vertebrates they, surprisingly, come off the front where the image is formed. A naive observer would think this to be a poor arrangement because the neurons might interfere with the light falling on the retina. The Darwinists say, with their usual theological argument, that if it were designed by an omniscient Creator, it would surely have the nerve connections coming out of the back side of the retina. Since they come off the front side, against one’s expectation, Darwinists conclude there is no omniscient Creator and therefore evolution must be true.  …
With regard to the inverted retina, it has recently been discovered that, rather than being a dumb design, it is actually remarkably clever. The cleverness is not in the neurons on the image side of the retina, but in the glial cells, which always accompany neurons. The neurons are transparent and do not interfere with the passage of light, but the glial cells aid the process of vision by channeling the light. The glial cells of the retina are long and thin and propagate light as in an optical fiber (Franze et al. 2007), and have been called “ingeniously designed light collectors.” Amichai Labin and Ezra Ribak of the physics department of the Technion (Israel Institute of Technology) have shown by simulation and calculation that the glial cells improve the optical resolution of the retina and compensate for chromatic aberration (Labin and Ribak 2010). Had the optic neurons come off the back side of the retina, these advantages would not have accrued.
 Of course, they have no precise idea of how evolution could have led to the development of the retina. Typical of their vague arguments, they don’t know what mutations would be necessary to generate the nerve network, or if it could be done at all through a sequence of adaptive mutations.
More on “backwards” eye wiring, if of interest:
2011: A New Article in Salvo Magazine Rebuts Objections that the Vertebrate Eye is Poorly Designed
Dawkins concedes that the optic nerve’s impact on vision is “probably not much,” but the negative effect is even less than he admits. Only if you cover one eye and stare directly at a fixed point does a tiny “blind spot” appear in your peripheral vision as a result of the optic nerve covering the retina. When both eyes are functional, the brain compensates for the blind spot by meshing the visual fields of both eyes. Under normal circumstances, the nerves’ wiring does nothing to hinder vision.
Nonetheless, Dawkins argues that even if the design works, it would “offend any tidy-minded engineer.” But the overall design of the eye actually optimizes visual acuity.
To achieve the high-quality vision that vertebrates need, retinal cells require a large blood supply. By facing the photoreceptor cells toward the back of the retina, and extending the optic nerve out over them, the cells are able to plug directly into the blood vessels that feed the eye, maximizing access to blood.
Yes, there’s that concept of optimization…
2014: Phys.org: Specialized Retinal Cells Are a “Design Feature,” Showing that the Argument for Suboptimal Design of the Eye “Is Folly”
Now a new paper in Nature Communications, “Müller cells separate between wavelengths to improve day vision with minimal effect upon night vision,” has expanded upon this research, further showing the eye’s optimal design. According to the paper, Müller cells not only act as optical fibers to direct incoming light through the optic nerve, but are fine-tuned to specific wavelengths to ensure that light reaches the proper retinal cells.
See also: Further to Lee Spetner’s comments on the (correct) wiring of the vertebrate eye* (sometimes used as a claim for “poor design”), over at Creation-Evolution Headlines, there are some recent articles on the subject, with lots of links:
Two Evolutionary Evidences Debunked (7/23/14)
This evolutionary argument began to unravel in 2007 when researchers found that Müller cells, penetrating the thicket of blood vessels in the human retina, actually provide near-ideal vision by acting as wave guides to the individual photoreceptors—providing better performance than could be had if the rods and cones were in front of the blood vessels (see 5/02/2007 and subsequent research reported 5/07/2010 about additional vision enhancements provided by the Müller cells)
Backward Wiring of Eye Retina Confirmed as Optimal (2/27/15)
On The Conversation today, Erez Ribak in person has explained why the eye is “wired backwards” for several good reasons. What’s new is how the retina optimizes reception by color. Since blue predominates in daytime light, we don’t need it amplified, so most of the blue wavelengths scatter in the eyeball and retinal blood vessels to the rods. That’s also why there are fewer blue-sensitive cones in the retina. Green and red, however, need amplification. Experiments with guinea pig retinas and computer models showed some surprises: …
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