I also found this article to be pretty interesting. Bad Designs?
Bad Design in the Human Eye?
The vertebrate eye is quite an exceptional organ in terms of its function. Light passes through the cornea, then through the lens where it is focused on the retina, which contains the photoreceptors (rods and cones) for detecting this light (see diagram to right). Each rod and cone that receives light fires a signal to the neural apparatus, which transmits the signal to the optic nerve, which goes to the brain for processing. The brain does some fancy processing, including inverting the image and interpreting what is seen (this is a whole other story that cannot be covered here).
The invertebrate eye is much simpler and is quite different, especially in the design of its retina. The invertebrate retina is composed of the photoreceptors, which face the incoming light, followed by the neural layer, and the underlying layers that supply nutrients and oxygen through a capillary bed. However, the vertebrate retina is said to be "inverted," since the neural layers face the light and the photoreceptor cells actually face away from the incident light. Evolutionists say that this arrangement was the result of improvised evolution in which obvious errors in "design" were accommodated through successive mutational alterations to make the apparatus work in a functional manner. According to Richard Dawkins, a leading proponent of evolution:
"Any engineer would naturally assume that the photocells would point towards the light, with their wires leading backwards towards the brain. He would laugh at any suggestion that the photocells might point away, from the light, with their wires departing on the side nearest the light. Yet this is exactly what happens in all vertebrate retinas. Each photocell is, in effect, wired in backwards, with its wire sticking out on the side nearest the light. The wire has to travel over the surface of the retina to a point where it dives through a hole in the retina (the so-called �blind spot�) to join the optic nerve. This means that the light, instead of being granted an unrestricted passage to the photocells, has to pass through a forest of connecting wires, presumably suffering at least some attenuation and distortion (actually, probably not much but, still, it is the principle of the thing that would offend any tidy-minded engineer). I don�t know the exact explanation for this strange state of affairs. The relevant period of evolution is so long ago." 4
Dawkins doesn't know why the vertebrate retina is designed this way because he doesn't really understand how the eye works. In fact, the retina is designed with slightly suboptimal light gathering abilities so that it will be functional for at least several decades. If it were designed according to Dawkins' "tidy-minded engineer," it would not work at all, as we shall see.
First, we need a short introduction to the physics of light. The electromagnetic spectrum emitted by the sun is composed of many different wavelengths, a small percentage of which are visible to our eyes (370-730 nanometers). The near-visible wavelengths include the longer wavelengths (infrared) and the shorter wavelengths (ultraviolet). The amount of energy within each wavelength is inversely proportional to the wavelength. Therefore, electromagnetic energy that consists of shorter wavelengths (e.g., ultraviolet light) is more energetic.
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Neural
Layer |
Rods and
Cones |
RPE
Choroid |
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Although the visual apparatus cannot detect the high energy wavelengths, it is still affected by them, since the entire system is exposed to the full spectrum. In contrast, the rest of the body is protected from high energy light by pigment (melanin) in the skin. Even so, a lifetime exposure of the skin cells to this light can result in DNA damage, which may lead to the development of cancers. The eye contains a special layer of cells, the Retinal Pigment Epithelium (RPE), which has complex mechanisms for dealing with toxic molecules and free radicals produced by the action of light. Specific enzymes such as the superoxide dismutases, catalases, and peroxidases are present to eliminate potentially harmful molecules such as superoxide and hydrogen peroxide. Antioxidants such as a-tocopherol (vitamin E) and ascorbic acid (vitamin C) are available to reduce oxidative damage.
Because of continuous damage caused by light, the discs (along with the photopigments) of the photoreceptor cells are continuously replaced by the RPE. 5, 6 If this were not the case, the photoreceptors would quickly accumulate fatal defects that would prohibit their function. In addition, the RPE cells contain the pigment melanin, which absorbs stray and scattered light to improve visual acuity. The RPE is in contact with the choroid layer, which contains a very large capillary bed, which has the largest blood flow per gram of any tissue in the body. Why is the blood flow so high in the choroid? Since the RPE and photoreceptor cells are in constant regeneration, they require a high rate of exchange of oxygen and nutrients. In addition, it appears that the high rate of blood flow is required to remove heat from the retina to prevent damage resulting from focused light (the old magnifying glass in the Sun phenomenon). 7
So why is Dawkins' "tidy-minded engineer" design such a bad idea? Dawkins thinks that the neural layer should be under the photoreceptors, putting them between the photoreceptors and the choroid. Where would the RPE (which is required to regenerate the photoreceptors) go? If it were between the neural layer and the choroid, it would be too far away from the photoreceptors to constantly regenerate them. In addition, this design would put another layer between the photoreceptors and their blood supply, reducing the exchange of oxygen and nutrients, and minimizing the effectiveness of the choroid in removing heat from the receptors. Dawkins' idea of "good" evolution would prevent the photoreceptors from being regenerated and would likely lead to heat damage. Such a design would certainly fail within the first year of use. It's a good thing that God does not design the way evolutionists would!
More information on the design of the eye can be found at the links below. 8-10
The vertebrate eye is quite an exceptional organ in terms of its function. Light passes through the cornea, then through the lens where it is focused on the retina, which contains the photoreceptors (rods and cones) for detecting this light (see diagram to right). Each rod and cone that receives light fires a signal to the neural apparatus, which transmits the signal to the optic nerve, which goes to the brain for processing. The brain does some fancy processing, including inverting the image and interpreting what is seen (this is a whole other story that cannot be covered here).