Eye

The eye is the visual system organ that provides sight or vision; one of the most important senses for living organisms. Eyes detect light, and send electrical impulses along the optic nerve to the visual and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. Image-resolving eyes are present in vertebrates, cnidarians, mollusks, annelids and arthropods.

The complexity and functionality of the eye is an engineering marvel that rivals anything made by human hands. Such precision is but one of many example of intelligent design that can be clearly seen in living organisms, illustrating God's invisible qualities—his eternal power. Even Charles Darwin recognized that the eye was imminently complex and admitted that attempting to explain its origin through natural selection seemed absurd.

To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree.

Vertebrate

 * Main Article: Human eye

Vertebrate eyes are are positioned at the location that is most comfortable for vision, and enables us to control and direct our bodies and limbs in an optimum way. The eyeballs rest upon a protective cushion of fat in the socket, are encircled with special tissues, and joined to the skull by six bony extensions. They are protected against external harm by the brow ridges, by the arch of the nose and the cheekbones. These surrounding bones and tissues are called the orbit. The movement of the eye is accomplished by a variety of parts. Each muscle and nerve in the eye has a unique role, and coordinates movement with the brain to help us see and function.

At the back of the retina are a number of rod-shaped and cone-shaped photoreceptor cells. These cells convert received light into electrical signals. Because of their shape as observed under a microscope, they are called rods and cones. There are 6,000,000 cones and 120,000,000 rods in the eye. That is a ratio of nearly 20 rods to every cone. Rods can respond by forming a black-and-white image, whereas cones perceive color. The rods and cones convert light waves into electrical energy. There are four perceptions that the retina can interpret: light, shape, contrast, and color. The rod cells are able to perceive more light than do the cone cells. Because of the rods we can see at twilight. In brighter conditions, the cone cells come into play perceiving the shape of objects giving us the extremely important ability to differentiate between areas that are not clearly separated.

Compound
The compound eye is one of the most complex and diverse organs. There are ten distinct types of compound eyes, nine of which can be found in Crustaceans, and four distinct types are present in the decapod subgroup alone. Apposition eyes (which form multiple inverted images) are more common in crustaceans with the reflecting superposition type (which form a single erect image) typical in the decapods.

Apposition
Apposition eyes work by gathering a number of images, one from each eye, and combining them in the brain, with each eye typically contributing a single point of information. The typical apposition eye has a lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium. In the other kind of apposition eye, found in the Strepsiptera, lenses are not fused to one another, and each forms an entire image; these images are combined in the brain. This is called the schizochroal compound eye or the neural superposition eye. Because images are combined additively, this arrangement allows vision under lower light levels.

Reflective superposition


The unique design of the lobster eye has been intensely studied to help understand how it allows some organisms to see in low light and murky waters. Rather than bending (refracting) the light to focus the image on the retina, several of the long-bodied decapod crustaceans (shrimps, prawns, crayfish and lobsters) possess “reflecting” compound eyes. Unlike the more common compound eyes of insects, which have hexagonal facets, this unique eye design incorporates square facets that are arranged radially forming an optic array with a 180° field of view. The geometric assemblage of facets has all of the hallmarks of intelligent design and defies attempts to explain it through natural mechanisms.

Simply put, these facets are tiny square-shaped tubes with walls that act as mirrors to reflect the incoming light. The walls of each facet are perfectly aligned so that the reflected light is focused toward the receptor layer flawlessly so that they all merge at the same point. The design creates an intensified, superpositioned image because the light from many facets combines to form a single image. As many as 3000 reflective facets are found in some species such as the Norway lobster (Nephrops norvegicus), and increases in sensitivity up to 1000 above the more common apposition type eye (where light remains within a single facet/ommatidium).

The ability of the decapod’s eye to intensify an image that is captured from a broad field of view has intrigued engineers since the mechanism was first made known. Investigating biological systems or processes for potential use in technology is rapidly expanding field known as biomimicry. Several technological developments are now based on the unique geometric design of the lobster eye (see Lobster eye biomimicry). Researchers have developed a cosmic imaging device for use on space satellites, and a handheld imaging system was built that can view through walls of various thicknesses and materials, and identify contents.

Evolution
Evolutionists have attempted to construct phylogenies (evolutionary relationships) by comparing the types of compound eyes present in existing groups. It is generally assumed that the apposition eyes evolved first since they are the most common type of compound eye, they are also present in larval stages of all decapods, and possessed by all “lower crustaceans”, such as the trilobite. The advanced reflecting superposition optics that inspired biomimicry applications is assumed to have developed by undirected Darwinian processes in an ancient common ancestor of the decapods. However, no specific mechanisms for its development have yet been put forth and experts admit that the overall structure of the eye would have to be radically transformed or non-functioning intermediates would result.

According to Edward Gaten, University of Leicester: The evolution of superposition eyes from the apposition eyes found in primitive crustaceans poses a particular problem. The apposition eye produces multiple inverted images whereas in the superposition eye a single erect image is present. To make this transition without going via non-functioning intermediates requires a continuing correction of the focusing properties of the dioptric apparatus so that light leaving the crystalline cone is either afocal or is focused onto the rhabdom layer.

News: World's oldest complex eye found in Australian fossil Eyes just like those of modern insects and crustaceans, with thousands of individual lenses were recently discovered in Cambrian strata, although previously thought not to have evolved for at least another 40 million years, Herald Sun, June 30, 2011.