Theory of Intelligent Design, the best explanation of Origins

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Theory of Intelligent Design, the best explanation of Origins » Intelligent Design » Is the eye bad designed ?

Is the eye bad designed ?

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1 Is the eye bad designed ? on Sun Apr 20, 2014 7:35 am


Is Our ‘Inverted’ Retina Really ‘Bad Design’?

As it turns out, the supposed problems Dawkins finds with the inverted retina become actual advantages in light of recent research published by Kristian Franze et. al., in the May 2007 issue of PNAS . As it turns out, "Muller cells are living optical fibers in the vertebrate retina."  Consider the observations and conclusions of the authors in the following abstract of their paper:

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

"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."

inverted retinas seem to have some at least marginal if not significant advantages based on the needs of their owners.  We also have the evidence that the best eyes in the world for image detection and interpretation are all inverted as far as their retinal organization.  As far as the disadvantages are concerned, they are generally not of practical significance in comparison to overall relative function.  Even Dawkins seems to admit that his uneasiness is mostly one of aesthetics.  Consider the following admission from Dawkins:

With one exception, all the eyes I have so far illustrated have had their photocells in front of the nerves connecting them to the brain. This is the obvious way to do it, but it is not universal. The flatworm keeps its photocells apparently on the wrong side of their connecting nerves. So does our own vertebrate eye. The photocells point backwards, away from the light. This is not as silly as it sounds. Since they are very tiny and transparent, it doesn't much matter which way they point: most photons will go straight through and then run the gauntlet of pigment-laden baffles waiting to catch them.

Is Our ‘Inverted’ Retina Really ‘Bad Design’?


Light at various wavelengths is capable of very damaging effects on biological machinery. The retina, besides being an extremely sophisticated transducer and image processor, is clearly designed to withstand the toxic and heating effects of light.  The eye is well equipped to protect the retina against radiation we normally encounter in everyday life.  Besides the almost complete exclusion of ultraviolet radiation by the cornea and the lens together, the retina itself is endowed with a number of additional mechanisms to protect against such damage:

   The retinal pigment epithelium produces substances which combat the damaging chemical by-products of light radiation.

   The retinal pigment epithelium plays an essential part sustaining the photoreceptors.  This includes recycling and metabolising their products, thereby renewing them in the face of continual wear from light bombardment.

   The central retina is permeated with xanthophyll pigment which filters and absorbs short-wavelength visible light.

The photoreceptors thus need to be in intimate contact with the retinal pigment epithelium, which is opaque.  The retinal pigment epithelium, in turn, needs to be in intimate contact with the choroid (also opaque) both to satisfy its nutritional requirements and to prevent (by means of the heat sink effect of its massive blood flow) overheating of the retina from focused light.

If the human retina were ‘wired’ the other way around (the verted configuration), as evolutionists such as Dawkins propose,2 these two opaque layers would have to be interposed in the path of light to the photoreceptors which would leave them in darkness!

Thus I suggest that the need for protection against light-induced damage, which a verted retina in our natural environment could not provide to the same degree, is a major, if not the major reason for the existence of the inverted configuration of the retina.

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2 Re: Is the eye bad designed ? on Sun Apr 20, 2014 9:57 am



A. M. Labin and E. N. Ribak, “Retinal Glial Cells Enhance Human Vision Acuity,” Physical Review Letters 104 (2010).


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.

Much of atheism stems from an understandable enthusiasm to do away with seemingly archaic superstitions, but in haste, expresses some astonishing ignorance: a typical claim in Dawkins’ lectures, echoed even by thinkers such as Christopher Hitchens (perhaps due to the tendency of intellectuals to rely on the accuracy of other specialists) is that the backwards facing retina found in mammals is a poor design, and therefore evidence of random evolution.

As is shown in The Willing Pupil, this claim is completely incorrect: the more intuitively obvious forward-facing arrangement would be hopelssly inadequate in any long-lived organism exposed to sunlight.

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3 Re: Is the eye bad designed ? on Mon Jul 07, 2014 4:14 am



One result is a blind spot in our visual field, leading the vertebrate retina to be listed among evolution’s biggest “mistakes”.

In 2007 researchers reported that the glial cells act as optical fibres for the rods and cones. New findings suggest that sending light via the Müller cells act as light filters, keeping images clearnd that the intrinsic optical properties of Müller cells seemed to be tuned to visible light. The cells also seem to help keep colours in focus. Müller cells’ wide tops allow them to “collect” any separated colours and refocus them onto the same cone cell, ensuring that all the colours from an image are in focus.

However, Kenneth Miller, cautions that this doesn’t mean that the backwards retina itself helps us to see.”

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4 Re: Is the eye bad designed ? on Fri Aug 08, 2014 5:02 pm



The retina can detect a single photon of light, and it’s impossible to improve on this sensitivity! More than that, it has a dynamic range of 10 billion (1010) to one; that is, it will still work well in an intensity of 10 billion photons. Modern photographic film has a dynamic range of only 1,000 to one. Even specialist equipment hasn’t anywhere near the dynamic range of the eye, and I have considerable experience in state-of-the-art supersensitive photomultipliers.

Another amazing design feature of the retina is the signal processing that occurs even before the information is transmitted to the brain, in the retinal layers between the ganglion cells and the photoreceptors. For example, a process called edge extraction enhances the recognition of edges of objects. Dr John Stevens, an associate professor of physiology and biomedical engineering, pointed out that it would take ‘a minimum of a hundred years of Cray [supercomputer] time to simulate what takes place in your eye many times each second.’1 And the retina’s analog computing needs far less power than the digital supercomputers and is elegant in its simplicity. Once again, the eye outstrips any human technology

The idea that the eye is wired backward comes from a lack of knowledge of eye function and anatomy.

He explained that the nerves could not go behind the eye, because that space is reserved for the choroid, which provides the rich blood supply needed for the very metabolically active retinal pigment epithelium (RPE). This is necessary to regenerate the photoreceptors, and to absorb excess heat. So it is necessary for the nerves to go in front instead. The claim on the program that they interfere with the image is blatantly false, because the nerves are virtually transparent because of their small size and also having about the same refractive index as the surrounding vitreous humor. In fact, what limits the eye’s resolution is the diffraction of light waves at the pupil (proportional to the wavelength and inversely proportional to the pupil’s size), so alleged improvements of the retina would make no difference.

Blind spot, bad design ?

the blind spot occupies only 0.25% of the visual field, and is far (15°) from the visual axis so that the visual acuity of the region is only about 15% of the foveola, the most sensitive area of the retina right on the visual axis. So the alleged defect is only theoretical, not practical. The blind spot is not considered handicap enough to stop a one-eyed person from driving a private motor vehicle.

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5 Mystery of the reverse-wired eyeball solved on Sat Feb 28, 2015 12:32 pm


Mystery of the reverse-wired eyeball solved

From a practical standpoint, the wiring of the human eye - a product of our evolutionary baggage - doesn't make a lot of sense. In vertebrates, photoreceptors are located behind the neurons in the back of the eye - resulting in light scattering by the nervous fibers and blurring of our vision. Recently, researchers at the Technion - Israel Institute of Technology have confirmed the biological purpose for this seemingly counterintuitive setup.
"The retina is not just the simple detector and neural image processor, as believed until today," said Erez Ribak, a professor at the Technion - Israel Institute of Technology. "Its optical structure is optimized for our vision purposes." Ribak and his co-authors will describe their work during the 2015 American Physical Society March Meeting, on Thursday, March 5 in San Antonio, Texas.
Ribak's interest in the optical structure of the retina stems from his previous work applying astrophysics and astronomy techniques to improve the ability of scientists and ophthalmologists to view the retina at high detail.
Previous experiments with mice had suggested that Müller glia cells, a type of metabolic cell that crosses the retina, play an essential role in guiding and focusing light scattered throughout the retina. To test this, Ribak and his colleagues ran computer simulations and in-vitro experiments in a mouse model to determine whether colors would be concentrated in these metabolic cells. They then used confocal microscopy to produce three-dimensional views of the retinal tissue, and found that the cells were indeed concentrating light into the photoreceptors.
"For the first time, we've explained why the retina is built backwards, with the neurons in front of the photoreceptors, rather than behind them," Ribak said.
Future research for Ribak and his colleagues includes using water-filled goggles to reduce corneal aberrations, allowing observers to gain a finer view of the retina at depth.

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6 Re: Is the eye bad designed ? on Wed Mar 18, 2015 7:15 pm



The human eye is optimised to have good colour vision at day and high sensitivity at night. But until recently it seemed as if the cells in the retina were wired the wrong way round, with light travelling through a mass of neurons before it reaches the light-detecting rod and cone cells. New research presented at a meeting of the American Physical Society has uncovered a remarkable vision-enhancing function for this puzzling structure.

About a century ago, the fine structure of the retina was discovered. The retina is the light-sensitive part of the eye, lining the inside of the eyeball. The back of the retina contains cones to sense the colours red, green and blue. Spread among the cones are rods, which are much more light-sensitive than cones, but which are colour-blind.

Before arriving at the cones and rods, light must traverse the full thickness of the retina, with its layers of neurons and cell nuclei. These neurons process the image information and transmit it to the brain, but until recently it has not been clear why these cells lie in front of the cones and rods, not behind them. This is a long-standing puzzle, even more so since the same structure, of neurons before light detectors, exists in all vertebrates, showing evolutionary stability.

Researchers in Leipzig found that glial cells, which also span the retinal depth and connect to the cones, have an interesting attribute. These cells are essential for metabolism, but they are also denser than other cells in the retina. In the transparent retina, this higher density (and corresponding refractive index) means that glial cells can guide light, just like fibre-optic cables.

Selective vision
In view of this, my colleague Amichai Labin and I built a model of the retina, and showed that the directional of glial cells helps increase the clarity of human vision. But we also noticed something rather curious: the colours that best passed through the glial cells were green to red, which the eye needs most for daytime vision. The eye usually receives too much blue—and thus has fewer blue-sensitive cones.

Further computer simulations showed that green and red are concentrated five to ten times more by the glial cells, and into their respective cones, than blue light. Instead, excess blue light gets scattered to the surrounding rods.

This surprising result of the simulation now needed an experimental proof. With colleagues at the Technion Medical School, we tested how light crosses guinea pig retinas. Like humans, these animals are active during the day and their retinal structure has been well-characterised, which allowed us to simulate their eyes just as we had done for humans. Then we passed light through their retinas and, at the same time, scanned them with a microscope in three dimensions. This we did for 27 colours in the visible spectrum.

The result was easy to notice: in each layer of the retina we saw that the light was not scattered evenly, but concentrated in a few spots. These spots were continued from layer to layer, thus creating elongated columns of light leading from the entrance of the retina down to the cones at the detection layer. Light was concentrated in these columns up to ten times, compared to the average intensity.

Even more interesting was the fact that the colours that were best guided by the glial cells matched nicely with the colours of the cones. The cones are not as sensitive as the rods, so this additional light allowed them to function better—even under lower light levels. Meanwhile, the bluer light, that was not well-captured in the glial cells, was scattered onto the rods in its vicinity.

These results mean that the retina of the eye has been optimised so that the sizes and densities of glial cells match the colours to which the eye is sensitive (which is in itself an optimisation process suited to our needs). This optimisation is such that colour vision during the day is enhanced, while night-time vision suffers very little. The effect also works best when the pupils are contracted at high illumination, further adding to the clarity of our colour vision.

Erez Ribak, at the Israel Institute of Technology, does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

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