In our previous article where we discussed the mind-boggling complexity of our eyes’ retinas. We learned about the ten separate layers of cells, but we did not elaborate on the intricacies of their creation. We also learned how the substance in the cone cells, called rhodopsin, is destroyed on exposure to light and then regenerated in the dark. We thus touched on the wisdom behind the existence of both night and day.

The destruction of rhodopsin is caused by the generation of electricity after its contact with light. This electric impulse is transmitted from cones and rods to either horizontal or bipolar (having two poles) cells. The section between these two different layers of cells is called the outer plexiform layer, where horizontal cells receive electric impulses from rods and cones, and carry them to neighboring bipolar cells. The horizontal cells are also charged with transmitting electricity horizontally between rod and cone cells. The signals make it possible for shapes to be carried to the central nervous system in an appropriate contrast. Other signals are blocked so that the borders of the place of contact with light can be clarified in the brain, which does not receive an excessive load of signals. If it were not for these cells, it would be harder to perceive borders because the line of difference between two different colors would not become clear.

Bipolar cells have two opposite poles. They are created as one of two types, in accordance with their functions: one amplifies generated electric impulses, while the other inhibits the transmission of excessive impulses from around the perceived object to the brain. Bipolar cells provide the contrast necessary for making borders clear. They make clear vision possible, and yet most people have never heard of this wondrous gift inside their retinas!

How is contrast enabled?

Thanks to an innate ability, our brain does not occupy itself with regions that have the same color or the same light. It will not be stimulated much if, for example, a wall is completely white or a car is bright red all over. If, however, there are other colors on the wall, say, a white moon or star on a red background, then there will be more stimulation in the brain. Suppose we place the shape of a crescent on the wall. The stimulated parts of the brain will lie along the sharp ends of the crescent, not in the inside or outside of it. The stimulation in the brain is less associated with non-contrasting regions than contrasts in view. The higher the contrast, i.e. the greater the difference between light and dark areas, the greater the degree of stimulation.

Amacrine cells in the inner plexiform layer of the retina enable horizontal transmission. There are up to 30 different types of these cells, and they carry out at least five to six functions. For instance, one type of Amacrine cell transmits electric impulses from cones and rods to bipolar cells, then to other Amacrine cells, then to ganglion cells, and finally to the brain.

Another type of Amacrine cell responds strongly to the onset of the visual signal, while another to its completion. One other type reveals the difference in light intensity regardless of direction, while still others respond to the movement of a light point in a certain direction in the retina, causing a perception in the brain as to the direction of the light.

Further research may reveal yet more functions. Amacrine cells might have such functions as regulating the intensity of electric impulses specific to each wavelength and generating different levels of impulses for moving or stationary objects.

The function of the ganglion cells in the innermost layer of the retina is to help ensure that the electric impulse generated and corrected in the retina is eventually transmitted to the brain. Three distinct ganglion cells are identified in the retina. These cells are represented with the letters W, X, and Y. W cells are assigned the task of transmitting signals from rod cells, which produce black and white visual signals in the dark. Making up about 40 percent of all ganglion cells, they have diameters of less than 10 micrometers and transmit signals at a speed of 8 m/sec. It is evident that these cells are assigned the task of perceiving objects in the dark as rough, vague shapes.

X cells, on the other hand, transmit electric impulses to the brain, creating precise color pictures of objects. Making up 55 percent of ganglion cells, they have midsize diameters (10-15 micrometers) and transmit signals at a speed of 14 m/sec.

The largest of ganglion cells (with diameters as long as 35 micrometers), Y cells are assigned the task of transmitting instant changes in sight. Making up only 5 percent of ganglion cells, they send signals at speeds of 50 m/sec.

Sending intense signals in split seconds, Y cells inform the central nervous system immediately in case of a threat or an unusual encounter. When our body or eyes face a threat, these cells help protect us by warning the brain to move away from the threat or close our eyelids rapidly. If it were not for these cells, we would not be able to reflexively close our eyes and thus protect them. It’s incredible to ponder how complex these systems are – and how perfectly they’ve been created.

Between layers of cells there also lie layers of network that house neurons and their connections (synapses). These cells too have subgroups trained to carry out specific tasks. All of these cells are built according to certain specifications so that they can transmit stimuli to the brain when they receive light. Extremely severe visual problems develop when even a single layer of these types of cells is missing. Every one of the layers in our eyes is immensely special, and it is hard to imagine them to have been randomly placed there. It should be born in mind that this article simply skipped numerous elements of the retina and their chemical functions. Taking the precise measurements and mechanisms into account, we can only feel greater awe and love in the face of the incredible art devoted to the creation.

The first article can be found at https://fountainmagazine.com/2018/issue-126-november-december-2018/retina-the-mind-boggler

The eye is a miracle as it is. Even though we have a rough understanding of its basic anatomy, we are confronted with a much more complex miracle when we venture into the intricacies of its anatomy and the physiology of the act of seeing. We have theories about the many details – such as the perception and representation of mental images and their storage in the memory – but we still do not exactly know how the act of seeing works.

One of the most mysterious layers of the eye, the retina has an elaborate structure with a slew of functions. Not every eye surgeon dares touch the retina, which houses the most sensitive and special cellular layers. It is a three dimensional, crescent-shaped structure located in the back of the eye and is made up of ten super thin layers of cells that span the exterior part of the eye abutting the veins and its interiors.

Retinal layers

The ten layers that form the retina are:

1. Pigment (coloring matter) layer
2. Layer of rods and cones
3. External limiting membrane
4. Outer nuclear layer comprising rod and cone cells
5. Outer plexiform layer
6. Inner nuclear layer
7. Inner plexiform layer
8. Ganglion layer
9. Nerve fiber layer
10. Inner limiting membrane

These layers are incredibly sensitive and elaborate, and studying their intricate structure give a sense of awe.

Light for sight

Light first arrives at and penetrates through the cornea, the living glassy layer at the outermost layer of the eye. It then goes through the frontal fluid (aquesous humor) and the aperture called the pupil (pupilla). It hits the internal wall of the retina (the inside of the crescent) after passing through the lens in the eye and then the optic fluid filling up the chamber in the back. This alone is an interesting fact because it is much later that the light that gets to the retina reaches the layer of sensitive cone and rod cells, which perceive light. As these cone and rod cells are lined one after another for their protection, light reaches this outer layer of the retina after the ganglion cells, retinal layers and nuclear layers. Such an alignment leads to a reduction of acuity in the peripheral regions of the retina.

We have theories about the many details – such as the perception and representation of mental images and their storage in the memory – but we still do not exactly know how the act of seeing works

The central pit (fovea centralis)

The inner layers at the center of the retina, on the other hand, are drawn to the sides to prevent any loss in visual acuity. Resembling a pit, this section is much thinner than the periphery of the retina, so the layers that are likely to obstruct the passage of the light, and hence reduce visual acuity, are aligned specifically to allow light to directly hit cone and rod cells. Besides, cone cells, which are in charge of exact, colored sight, exist in this region, whereas rod cells, which are in charge of rough and uncolored (black and white) sight, do not.  The central pit where visual acuity is at its highest is for keen, colored, and exact sight. Why then is the rest of the retina not created for acute sight and why is this small section equipped with this ability?

As it turns out, if the entire retina had the ability to see keenly then it would not be possible for the eye to focus on a spot and accurately distinguish it from surrounding objects. If we could see the entire page of a book at a glance, for example, the lines would mix up in our brain. We would not be able to understand what we are reading. We normally start reading from the top of the written page and continue line by line as we focus on and take in each word. Our brain then can focus and perceive a single word accurately by restricting keen perception of the surrounding area.

The retinal pigment layer

The color black is known to absorb, not reflect, light. Thanks to such absorption, the layer made up of black pigments (melanin) or dyes prevents the reflection of light, which is crucial for visual acuity. This black substance functions like the black dye in the bellows of old cameras. If there were not any layer to absorb light, light would scatter off the wall inside the eyeball, thereby obscuring the sharpness between light and dark spots, which is essential for the formation of a clear image, and producing a blurry image due to the overall illumination of the retina.

People who lack this melanin pigment as a result of a genetic defect (Albinism disorder) have white hair, and they are oversensitive to light because the colored iris layer of the eye does not contain the melanin pigment, which refracts light. When an albino person enters a bright area, the light that hits the retina is reflected in all directions through the pigment-lacking retina and the white surfaces of the rigid layer underneath (sclera). Therefore, a ray of light that would normally stimulate a few cones or rods is scattered everywhere, stimulating all or most of the light receivers. As a result, visual acuity in albinos can only be between 20/100 and 20/200, even with the help of the best optical correction, which is a low value compared to 20/20 in normal sight. The joke that rabbits do not wear glasses because they eat carrots is based on the high concentration of vitamin A in this pigment, or black dye, layer of the eye. Indeed, vitamin A is a crucial factor for the health of these pigments.

Layer of rods and cones

Composed of 127 million light-sensitive receivers (photoreceptors), the retina is 0.2 mm thick at the yellow spot (macula lutea), where the image forms most clearly, and 0.1 mm thick at the edges of this area. The 120 million cylindrical rods in the retina are in charge of black and white sight (at twilight), and the 7 million tapered cones, of colored, colored and exact sight. The more common cylindrical rods are 50 µm (microns) in length and 1-5 µm in thickness. The less common cones are 40 µm (microns) in length and 3-5 µm in thickness.

The concentration of the cones increases toward the center of the retina and decreases toward the edges, to be outnumbered by the rods. In the cytoplasm of the cones and rods are stored substances that are sensitive to light (photosensitive) which break up when light contacts them and produce electricity in the cones and rods. In rods this chemical is called rhodopsin. In cones, on the other hand, are three substances corresponding to the colors red, green, and blue that are sensitive to the wavelengths of colored light. To be more exact, there are three separate cone cells that include one of these three substances. Chemically, the photosensitive substances in the cones are a little different from rhodopsins.

The destruction of rhodopsin by light energy

Rhodopsin, along with the color substances, fills up about 40% of rods and cones. They are made up of a protein called scotopsin and a molecule called retinene that is derived from vitamin A. When light energy is absorbed by rhodopsin or the color substances, rhodopsin starts to fade in as fast as one trillionth of a second. The underlying reason for this is that the electrons in the retinene (vitamin A) part of rhodopsin is activated by light, which alters the shape of the retinal molecule at a mind-boggling speed (one trillionth of a second). Extremely complicated and precise chemical and physical changes then take place. It is very difficult to monitor all of these biochemical changes, and they require specialization [1].

The regeneration of the rhodopsin destroyed by light

Rhodopsin destroyed by light is regenerated in the dark. Only in the twentieth century did we manage to partially identify the mechanism by which molecules with very specific geometric shapes decay at incredible speeds only to be regenerated later. It is wondrous that such knowledge and power are present in the cell allowing the light energy to destroy the molecule and the regeneration process is launched. The circulation between destruction and regeneration of the molecule continues throughout a lifetime [2]. Vitamin A is assigned a crucial task in the generation of rhodopsin in the dark. All-trans retinal is converted in the retina into all-trans retinol, which is then converted into 11-cys retinol with the help of an isomerase enzyme. Finally, 11-cys retinol is converted into 11-cys retinal, which in turn combines with scotopsin to form rhodopsin. Vitamin A is present both in the cytoplasm of rods and in the pigment layer of the retina. In this way, vitamin A is kept in reserve to be used for generations of new retinal. If, on the other hand, there is an excess of vitamin A in the retina, the excess amount is converted into retinal, by which the amount of light-sensitive pigment in the retina is lowered.

Night blindness

Night blindness appears in anyone who suffers a serious deficiency of vitamin A. Because there is a lack of vitamin A to be converted into retinal, rhodopsin amounts decrease dramatically. This disease is called night blindness as it is noticeable only in the dark or at night and does not affect sight during the day, due to the reduction of light for proper seeing. In daylight, however, cones can still be stimulated despite a similar decrease in color pigments. Night blindness typically only appears in people that have a low vitamin A diet because huge reserves of vitamin A are normally stored in the liver to be used for the eyes.

The human retina contains 400,000 light receptive cells per square millimeter. For comparison, this number is 680,000 in the retina of the owl, which needs to perceive even the slightest glow when hunting in the night. As another example, with 397,000 such cells the amount in the cat’s retina is almost the same as ours.

An average of 130 sight cells in the retina are connected to a ganglion (nerve node) cell. Constituting the nerve of sight, or the optic nerve (nervus opticus), every nerve fiber is connected to a ganglion cell. It takes about 15-60 seconds for the retinal optic nerves to adapt from dark to light, while it takes as long as 30-45 minutes to adapt from light to dark. The visual range of optic cells, i.e. the lowest and highest amount of light the eye can perceive, is between 10^-7 and 10⁶ nanometers. Light that is below or above this range is invisible to us because of its insufficient or overwhelming wavelength.

All the colors we see in the world are named according to the wavelengths absorbed and reflected by optic cells. The spectrum of the optic cells lies between red and violet, which is the limit of visible light for humans. Light with a wavelength of 400 nm is perceived as violet, while light with a wavelength of 760 nm is perceived as red. Our eyes cannot see infrared and ultraviolet light. Some animals, however, are known to see light beyond these limits. For example, we know that bees can see certain shades of ultraviolet light, which helps them find flowers to pollenate.

Clearly, it is not an easy job to elaborate on the divine art manifested in such a small area as the retina. Complicated structures and reactions that require specialization even to comprehend keep taking place smoothly every moment we look around. At least we can be thankful for this amazing gift of vision given to us free of charge so that we can recognize the universe.

Notes

[1] It causes the cys form of the molecule to change into the all-trans form. Although the all-trans form has the same chemical structure as the cys form, its chemical structure is different in that it is a flat rather than angular molecule. With the impact of light photons, the position of the molecule in space changes, yet its chemical composition remains the same. Because the position of the reactive regions of all-trans retinal no longer fit in with the reactive regions on scotopsin protein, the molecule is pulled off. The product that forms at that moment is batorhodopsins, which is a partly destroyed combination of all-trans retinal and scotopsin. An extremely unstable compound, batorhodopsin turns into lumirhodopsin in nanoseconds, into metarhodopsin I in microseconds, into metarhodopsin II in about one millisecond, and finally into decomposed products, scotopsin and all-trans retinal much more slowly (in seconds).

[2] The first step in the reformation of rhodopsin is the recycling of all-trans retinal into 11-cys retinal, which requires ATP energy and is catalyzed by retinal isomerase enzyme. Once created, 11-cys retinal combines with scotopsin to form rhodopsin.

How can animals in the wild hunt during the night as if it were day? A remarkable biological feature acts as a pair of “natural” night vision goggles.

Animals can move and even hunt in the pitch-dark of the night. How do these animals see comfortably in the dark? How are their eyes different from ours?

Anatomically, the eye consists of three layers called the Tunica fibrosa (outer layer), the Tunica vasculosa (mid layer), and the Tunica nervosa (retina). The outer layer of the eye is composed of the sclera and cornea; the middle section of choroidea, corpus ciliare, and the iris; and the inner section of the retina.

Light rays reflected off objects first pass through the eye’s translucent layer (the cornea), then into the black round part located in the front of the eye (pupillae, or pupil), and later go through the lenses. The colored section around the pupil, covered by smooth muscles, is in charge of regulating the amount of light entering the eye. The real and inverted image of an object is projected on the retina by the refraction of light through the lens; the image is transmitted to the optical center of the brain as a result of nerve cell stimulation via the optical nerves. Sight happens as a result of these causal chains.

Now, there is a twist to all this: the optical center in the brain accepts spots that do not emit light as black. For humans, this means a loss of sight. Black objects are not visible because they absorb and keep all the light reaching them.

How could these animals, without night vision goggles, see in pitch blackness despite having the same optical mechanisms as humans?

The answer to this question was hidden in an anatomic structure (tapetum lucidum) located in the eyes of some vertebrates. This special structure, lacking in humans, monkeys, squirrels, birds, red kangaroos, and some other mammals, is found in equines, ruminants, and many carnivores. This structure is located in the cytoplasm of the choroidea layers in between the innermost light sensitive ocular layer and sclera, and it acts like a biological reflector. With its crystalline composition of varying colors from golden yellow to white, tapetum lucidum is a wonder of creation. The eyes of these animals shine when a light source is projected due to the aforementioned structure.

The primary task of this formation is to reflect the light which is projected to the rear section of the eye again without absorbing it. This happens due to the crystalline makeup. Thus, lower light levels are enhanced by the repeated reflection in the eye, and sight is enabled for animals. The second job of Tapetum lucidum is to elevate the sensitivity of the retina to light in order to transmit signals with no stimulation strength to the optical center.

This reminds us of night vision goggles. Night vision cameras are electro-optical devices that strengthen the light that is present. Light enters this device through the lens and hits the charged cathode, which has a lot of high energy. The energy load hits the phosphorous screen where the image is focused after passing through the vacuum inside the charger. The image is an enhanced picture on the phosphorous screen and it is not visible directly through the object. Tapetum lucidum however, is such an artistic work that it cannot even be compared with the night vision systems of technology. While the lifespan of a night vision system is only 2,500–4,000 hours (104–167 days), animals with Tapetum lucidum can benefit from this for a lifetime. The newest night vision systems, with a maximum optic range of 30-120 meters, cannot provide sight under light conditions one fourth of the moon’s illumination strength, whereas animals with Tapetum lucidum can see objects hundreds of meters away in much dimmer light.

This isn’t the only example of how masterfully and diverse eyes can be. Damseflies have over 30,000 simple eyes, called ommatids; eagles can see their prey from thousands of feet above them.

By the principle that “certain things are appreciated best in their absence,” if we imagine a dark night in which we are unable to see anything and cannot even step a foot safely, we can perhaps understand that Tapetum lucidum is a great blessing for these animals.

Reference

Veterinary Ophthalmology (2004) 7, 1,11–22. Comparative morphology of the tapetum lucidum (among selected species), F. J. Ollivier,* D. A. Samuelson, D. E. Brooks, P. A.Lewis, M. E. Kallberg and A. M. Komáromy.

There are so many blessings in life, granted to us free of charge, which we take for granted. Eyesight, being able to see near and far distances, most certainly tops the list. But we do not have to be deprived of our sight in order to understand its wisdom and functioning, and to contemplate upon its true value and worth.

Years of research and hard work were dedicated to develop cameras and multi-featured objective lenses. Initially, one to three lens objective cameras were used for simple shots, whereas today, objectives with seven to ten lenses are being used to take better photographs from a snow drop falling onto a flower to a buzzing bee resting on a flower. I wonder to what extent human beings are aware of the pair of eyes that has been bestowed upon them by God, and its ability to see different colors and shapes both near and far. Unfortunately, as people who often understand the true value of things once they are lost, we understand the blessing of being able to see near after the age of forty when we cannot read the newspaper without glasses and when we cannot put a thread through a needle.

So why is it that we can still see far after the age of forty but fail to see near? In order to understand this we need to examine the structure of the eye and its functions.

The structure of the eye and the ability to see

The exterior part of the eye is made up of a translucent layer (cornea) at the front and a white protective layer (sclera) behind it. The vascular layer of the eye (uvea) is located in the middle of the sclera. The most inner part of the eye is made up of the retina, the light-sensitive layer of tissue responsible for converting light rays into electrical signals. The hole located in the center of the iris, the colored part of the eye, is called the pupil. Behind the pupil is the crystalline lens. For a clear vision, lights reflected from objects need to be focused on the central part of the retina (fovea). While cameras have lens systems to focus the image on the film, it is the cornea and crystalline lens that are responsible for the same function in the eye.

Refraction power of cornea is constant and around 43 diopters. The refraction power of the eye lens when resting is around 20 diopters. Light rays coming from outside refracts at a set ratio and manages to focus on the retina. The light rays coming at the retina are then coded into electrical signals. Afterwards these signals are routed towards related regions of the brain via optic nerves. Most of the stimuli relayed by the optical nerve arrive at the visual center of the brain (occipital cortex). These coded electrical signals then become vision when they reach the optical lobe of the brain.

The function of the lens and accommodation

The refraction power of both the cornea and the lens (43+20+63 diopters) is sufficient to focus an image on the retina when looking at objects farther than 6 meters. Extra refraction power is needed for closer distances in order to focus images on the retina. Mobile lens systems enable this job to take place in camera objectives. Since refraction power of the cornea in human eye does not change, this additional task of refraction is set to be provided by the ocular lens. It is built as a flexible structure without any blood vessels. Aqueous humor (lens fluid) which is secreted by the ciliary body is responsible for lens nourishment, removal of waste products and toning of the eye since the lens does not contain any blood vessels. This internal fluid has low oxygen concentration therefore the lens is made to derive its energy supply mostly from anaerobic metabolism.

The iris is positioned in a suitable place where it can change the shape of the internal lens behind the pupil. The lens in this special place is suspended into position via zonule of zinn ligaments attached to the eye as a ciliary body. The ciliary body contains ciliary muscles where zinn ligaments are attached. Only 0.5 mm of space exists between the lens and the ciliary body. Zinn ligaments are tight when ciliary muscles are resting and this enables a flatter configuration of the lens. Upon contraction of ciliary muscles, zinn ligaments become relaxed and the diameter of the lens decreases along with an increase in its thickness. Thicker lens becomes more globular and this increases its refractive power, thus enabling vision of the closer distances. This increase in refractive power of the lens in order to see closer objects is called “accommodation.” If the stimuli of the ciliary muscles expire, ciliary muscles then relax making zinn ligaments tighter, reducing thickness of the lens, making it flatter and therefore less refractive. This reshapes it to focus on distant objects for a clearer vision.

Accommodation mechanisms and loss of accommodation during aging

The vision blurs temporarily when one takes an immediate shift from staring at an object in the distance to another object nearby. As soon as this blurry image reaches the occipital cortex, stimuli generated here arrives first at the Edinger-Westphal nucleus via special nerve tracks and then to the ciliary muscles of the eye. In a very short time, this blurry vision is corrected and becomes clearer without us even noticing with optimal increase of refraction in the internal lens. In a time as short as 0.35 seconds, for thousands of times in a day, this mechanism is set to function in such a perfect manner to spur those thoughtful minds into reflection and wonder.

Accommodation ability is at its highest point in children and this feature of the eye decreases with age. Refractive power of the lens can increase up to 34 diopters with a 14 diopters accommodation power along with 20 diopters of resting refraction during childhood. This way, children can clearly see objects as close as 7 centimeters. Accommodation power decreases with age. It reduces to 4-8 diopters after the age of 40 and 2-3 diopters around the age of 50. It is widely accepted that refractive power disappears entirely after the age of 60.

In the advanced stages of aging, the eye lens loses its transparency, becomes cloudy as it develops cataract. Eye lens in this poor transparent stage is removed via cataract surgery, to be replaced with an artificial lens to carry out the refracting task. Unfortunately today, technology is still unable to produce an artificial lens that is capable of all the tasks that a human eye can perform. Artificial internal eye lenses that are used in surgeries today cannot carry out accommodation functions. Majority of these lenses can only focus on one point at a near or far distance. Newly developed multifocal lenses can utilize various mechanisms to see both near and far distances yet they are not in any position to replace the human lens completely.

Ocular motions when looking near and far

Thanks to ocular movements, we do not have to move our head constantly while looking around. The eye movement involving both eyes in which each eye moves in the same direction is referred to as version type movements. Another movement type is called vergence, and this is when both eyes move in opposite directions. Vergence type movements are a type of ocular motility coded in a special center part of the brain. It is called convergence because the eyes get closer to each other when looking at closer distances, and called divergence when both eyes focus on the same spot by directing away from each other. If eyes only moved in the same direction without this convergence mechanism, both eyes would not be able to focus on closer points and would not be able to develop three dimensional visions (depth perception).

In addition to accommodation and convergence, when we look closer, our pupils get smaller (Miosis). Light rays coming from outside objects get improved focus on the retina via this constriction of the pupils. This way, a clearer image is provided.

When we look closer, accommodation, convergence and miosis all happen at the same time in a synchronized manner to provide a clear vision. The details of these complicated chains of events have yet to be understood.

Conclusion

The fineness of refractive power of the eye with a single lens, accommodation ability and sensitive balances of ocular motility is only a few of the blessings of the eye granted to humankind. The ability to see near being at its peak during young ages when learning is most active is another dimension to this miracle. These wisdom-filled capacities given to the eye makes one ponder upon the importance of the eye for survival, in addition to being a reminder to those with an open mind and heart to gaze upon the natural world and contemplate upon the Almighty.

The four main functions required for life, namely the digestive, respiratory, circulatory, and excretory systems are all found in plants but performed by different organs. If these functions are non-existent the dynamism or the essence of existence that we call life will disappear and death is inevitable. If these four functions (digestion, circulation, respiration, and excretion) are in working order, it means an organism is alive but only at the level of plant life. To reach the animal level of life, in addition to the four main functions, functions like senses, nervous and muscular systems are also required.

If these functions fail, life continues, but at the level of plant life. We sometimes hear people saying “in a vegetative state.” When you hear this, people are usually talking about a person who has lost the use of the animal functions. He or she may be unable to see, feel, hear, or move. Intelligence, comprehension, will power, conscience and the many other special aspects of human beings cannot be compared with the essential functions of living; these are additional characteristics of being human which accompany the animal system of functions and emerge in relation to a person’s spirituality. This obviously does not mean that those who have lost their abilities are less human and they do not have any rights; on the contrary, it means to say that they are not responsible any more.

The focal points of sensory functions of sight, hearing, touch, taste, and smell are found within the head in the brain, which is the command center of our body and the most complex form of existence we know of in the universe. The brain is connected to the nervous system which communicates with all the organs in the human body. This is why the head is so precious; it is a very sensitive part of the body and has to be protected like a jeweler guards precious stones. If you tread on a nail, it may hurt for a while, but with treatment the wound can be cured. But if a nail were to penetrate someone’s head, this could damage any of the sensory functions or, God forbid, could even result in death.

As you have probably understood from our introduction, the head is firstly the center of animal functions then the focus point of the addition of the human senses. When you mention the head we are the first thing that comes to mind: the eyes. Did we hear you ask why? It’s because we are what you are reading these words with right now, and because you can see the beautiful creations of the universe with us-that’s why.

If my Creator had not created us and positioned us in the two cavities on your head, you would have no knowledge of the beauties of light, color, insects, flowers, roses or birds. You would be afraid to walk without us because you would have no idea where you are about to tread. The effect of sight can only be sent through us to your brain and reflected into your mind. The development of human knowledge would have been very delayed if God had not created us or the other sense organs because the only way to gain knowledge is through healthy sense organs. The sense organs are the only way of detecting and recognizing the characteristics of objects.

You need us to realize that water is transparent, apples are red, quinces are yellow and violets are purple, you need us to recognize your mothers, fathers and friends. You need us to eat, drink, read and write and so you do not bump into walls. What do you think will happen if we close our lids for ten seconds and you try to walk down the street? Try it if you want!

You see-it was harder than you thought. You were scared in case you bumped into something or fell over. Look, Peter, just take a deep breath and give praise to our Creator while our lids are closed tight, for you could not tolerate being in the dark for a mere ten seconds, so what if you never saw the light? Just think sometimes about people who are not as fortunate as you, who cannot see for one reason or another. Give praise to our Creator for not giving you such a trial, and pray for the patience of those friends who have been deprived of sight.

Yes, now we have come to our characteristics and delicate creation, so pay attention. When Darwin saw God’s magnificent skill in our creation, he realized that we could not have been just a coincidence or a self-made creation, and it was impossible for us to be a creation of unconscious nature. Due to the guilt he felt inside, he found it necessary to say that the idea that “the evolution of complex organs like the brain and the eye could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.”

There is no artificial optical device that can match the esthetics or precision of our creation. Our operating principles depend on the optical laws God Almighty has determined for the light. As a matter of fact, just by looking at our structure, human beings worked out the rules of optics, you made the simplest of cameras, and you went on to produce the most magnificent photographic cameras possible. But whatever you do, never try to compare one of us to those cameras you have invented or you may become rather embarrassed. Your cameras are a simple toy compared to us. From the time of the invention of the old, wooden box cameras that had to be covered with a black cloth up to the modern digital cameras of the present, 175 years have passed. Many people worked for years to bring cameras to such a perfect state. Can anyone claim that the old camera made of a wooden box and a lens evolved by itself and turned into the high-quality, digital cameras of today? With all the knowledge accumulated by hundreds of scientists over the years, can this invention really be called a coincidence? So, can we be a coincidence? Could the eyes of mollusks or insects make themselves evolve and transform into the eyes of humans? Of course not! But to understand this a little better you must pay attention to our structure.

We are globe-shaped and look like covered capsules with a multi-layered structure which is quite solid and supple (Figure 1). Each of us is approximately 24mm in diameter. We have an outer layer made of something called sclera (hard coating). We are protected by a strong cover made up of dense ligament fibers, and beneath this is the choroid layer (a layer of blood vessels), where the blood vessels nourishing us go into; this layer covers us completely like a network of vessels. In the middle of the eye is the retina which is a layer of film. It is located in the most precious place where our actual receivers of light reside. There are other layers which each have their own duty beneath these layers, but we won’t go into too much detail.

We each have a main casing that is round and has a dome-shaped surface which slightly protrudes. The center of the hard coating, the cornea, is transparent so that it will allow light to pass through. On the outer part of the transparent area is what they call the white of the eye, and the whole areas seen from the front is covered in a clear membrane (the conjunctiva) with mucus cells. This keeps us lubricated. So as to focus light rays, our cornea section is more curved than other sections. There is a tiny chamber behind this curved front and this is actually where the lens, which separates the main chamber, is found. In the front chamber between our lens and cornea is a transparent liquid, the iris, which gives us our color. The black hole in the center of the iris is called the pupil. The iris, which has a special structure of muscles, works like a curtain contracting and expanding our pupil in response to the brightness of light. If the light is powerful, it contracts to protect the retina from any damage, whereas if the light is dim, the iris expands the pupil to allow more light into the retina.

The fibers (zonules) that hold the lens suspended in place and the cluster of muscles (corpus ciliare), which changes our lens according to the focus distance, are in front of a layer of blood vessels. Our lens, which plays a role in focusing, changes shape and adjusts according to whether the focus point is near or at a distance by thinning and thickening. We do this with the help of the fibers that keep the lens suspended.

Behind the lens is a larger chamber filled with a jellylike, transparent liquid (vitreous humor). The pressure and consistency of the jellylike liquid ensure that we keep our round shape. There are photoreceptive cells in the shape of rods and cones which are sensitive to light in the dark chamber behind our retina. The visual images formed by the rays which pass through the cornea and lens to the retina are upside-down. There is a small pit in my retina where almost every cell has a light receptor cell. This is where your sharpest vision is formed, but that doesn’t mean that it is where you actually perceive the object you are looking at. Sight is what happens when a group of cells in the brain’s visual center is stimulated, and the images on our lens are comprehended. It is unbelievable how fast is the effect of the chemical and electro events on our light receptor cells. The effect of light is conveyed to your brain through the stimulation of electric signals in our receptors’ optic nerve where the actual vision is produced in the brain, so in a way we are just the means of vision.

Because we are such delicate and sensitive organs, our Creator placed us in the cavities within the bone structure of your head for protection. We fit in the very strong and secure structure comprising your chin bone, cheek bones, forehead bone, orbital bone (just around us, your eyes), nasal bone and occipital bone (at the rear and bottom of your skull), but this is not our only protective mechanism. We have top and bottom eyelids that we close to protect ourselves from oncoming dangers. The frequent blinking of our eyelids prevents our cornea from becoming dirty, just like the windscreen wipers of a car. Our eyelids are not just simple folds of skin, they are a secretion system of glands which continuously lubricate the inner part of your lashes and seize dirt and dust, turning them into harmless particles. When you feel emotion, the secretion produced by the tear glands between us and the nose fills the tear ducts, passes through the two canals, and gives us a good wash. But when you cry too much, the excess secretion empties through another canal, which also washes your nose.

As this system is complex, it can also go wrong sometimes. If you consider our many parts and our millions of cells you will clearly see the possibility that any one of our components may fail. However, our Creator has formed the eyes in most people’s heads without any defect or failure, so we can serve you with vision of the universe.

The Creator gives us something called illness so we are reminded of our weakness, a defect or failure which arises as an act of wisdom. Some illnesses, like diabetes, deficiency of vitamin A or atherosclerosis, may have a negative effect on us and even render us useless. We eyes also have some defects which occasionally appear, such as not being able to see at a distance, or close up. Focus defects are easily remedied with spectacles or lenses, but faults in the sensitive light receptor cells in the retina are more difficult to amend. The pressure of the liquid in our larger chamber must be correctly balanced. If this pressure increases too much, we will give you a great deal of pain due to what doctors call glaucoma. If we lose our transparency, your vision will become clouded by what is called a cataract. Apart from this, there are many viruses and bacteria that can cause infections and diseases, but the cells of your immune system are like soldiers who, with the Creator’s help, protect you from those bacteria and viruses.

Look, Peter! It would take pages and pages for us to explain ourselves to you, but we don’t really want to confuse you with even more anatomical information. Our whole aim is to explain the reasons for the creation of our parts, to astonish you with the wisdom and fine art of the Divine, so you will contemplate the wonders of creation and give praise to the Almighty for the blessings he has bestowed upon you. If we have been successful in achieving this, that would be the greatest reward we could ask for.

Irfan Yilmaz is a professor of biology at Dokuz Eylul University, Izmir, Turkey.

Optimality is defined as the “most favorable condition or greatest degree or amount possible under given circumstances.”¹ It denotes a general equilibrium in which no improvement in one part of a system is possible without a larger sacrifice in another part. Thus, optimality is not mere order; rather, it is the highest state of it. Every optimal state is also orderly, but every orderly situation does not have to be optimal. The houses that we live in are examples of this. It is quite clear that our houses are not the optimal design for a house, but they are still orderly, hence the result of intention and intelligence.

A common trend among today’s evolutionists is to consider apparent sub-optimality (or “poor design” as some put it) sufficient proof for the nonexistence of a designer (hence, God). Biologist Richard Dawkins, for example, contends that “evidence of telling imperfections” in design is important evidence that “no designer exists.”² However, there are serious problems with this argument. First, judgments about optimality require knowledge of the entire set of objectives and available means, whereas we have no complete knowledge of divine objectives as to the creation of anything. The Bible refers to this point in Job 38:4, “Where were you when I laid the foundations of the earth?” Similarly, the Qur’an states, “I did not make them witnesses of the creation of the heavens and the earth, nor of the creation of their own selfs” (Kahf 18:51). As we were not witnesses to the creation of the universe and human beings, we can never confidently say that something is “sub-optimal.” As one political scientist, George Tsebelis, has noted, cases of apparent sub-optimality are in fact cases of disagreement between “the actor” and “the observer”: “while the observer focuses attention on only one game, the actor is involved in a whole network of games”-what he calls nested games.³ What appears sub-optimal from the perspective of only one game is in fact optimal when the whole network of games is considered. Consequently, all conclusions about sub-optimality in the universe are unwarranted because as observers we have no comprehensive vision and understanding regarding God’s plans and objectives, which relate to multiple issues and platforms. Indeed, most sub-optimality arguments regarding creation are based on the assumed objectives of scientists, which do not necessarily correspond with the more complex and comprehensive objectives of God.

The sub-optimality arguments of evolutionists come in two forms: biological and theological. A famous example of the former is the “poor design” argument regarding the “inverted” arrangement of the vertebrate retina.⁴ Several neo-Darwinians have taken issue with the way retina is typically situated in vertebrates. The vertebrate retina is inverted in the sense that the photoreceptors sit at the back of the retina, so that light has to pass through a layer of neurons before it reaches them. Evolutionists have argued that this invertedness results in inefficiency in vertebrate vision, which is sufficient for them to conclude for the nonexistence of an all-knowing and all-powerful God. Yet, later research proved that in return for the above-mentioned negligible loss in vision, the current structure of the vertebrate retina is found to make possible better absorption of excess light⁵ and superior supply of blood to photoreceptors,⁶ both of which are essential for healthy vision. They are so essential that “[i]f the human retina were ‘wired’ the other way around,” concludes Peter Gurney, “the photoreceptors would be left in darkness.”⁷ This brings us to a verse in the Qur’an: “Were the truth to follow their lusts and fancies, the heavens and the earth and all those who live in them would certainly have gone to ruin” (Muminun 23:71).

A prominent example of the theological sub-optimality arguments of the evolutionists is the so-called “problem of evil,” which goes back to Darwin himself in the evolutionist tradition; Darwin had troubles with the apparently cruel acts in the animal world. Some of Darwin’s famous contemporary followers also take “the existence of human evil as well as of natural catastrophes and diseases” to mean that a benevolent God does not exist.⁸ For these evolutionists, the coexistence of evil and good is a sub-optimal situation and this is sufficient proof to reject the idea of a benevolent God. This argument suffers two ailments, though. The first and most ironic one is that the argument itself is more theology than science. From a scientific point of view, the question for which an answer is sought is whether the universe and everything inside it could have come into being by chance or not. The nature of God and how He ought to act are not questions that science seeks answers for. Second, these arguments stem from evolutionists’ own expectations regarding how the things should be, which are bounded by their strictly earthly considerations. When transcendental and other-worldly considerations are also taken into account, the problem almost evaporates into thin air. Throughout history the “problem of evil” (or theodicy) has been debated by hundreds of scholars in almost all religions. The reconciliation of worldly pains and sorrows with the mercy of a benevolent God has been one of the most challenging topics in the history of religion. Scholars of many religions have offered diverging explanations with varying degrees of consistency and persuasiveness. Some Christian explanations for human evil, for example, have rested on God’s wish to love and be loved out of free will. From this point of view, a genuine love requires a genuine free will, which results in evil actions as well good ones.⁹ Muslim scholars have also developed explanations that would account for all types of “evils.” First, similar to the previous Christian argument, human evil is argued to have been allowed for the realization of a genuine relationship between God and human beings. As for other “evils” such as natural catastrophes or diseases, most Muslim scholars do not view them as evils to start with. In the Muslim faith, everything that takes place happens out of a divine wisdom, which ultimately aims at the well-being of a believer in the afterlife. In this line of thinking, an adversity such as a disease can play three main possible divine roles. It is either a punishment for a believer’s sins or misbehavior in this world, which would replace a harsher punishment in the hereafter; or a test to be passed for spiritual development; or a tool to make a believer approach God by increasing his or her supplications meanwhile.¹⁰In each of these cases, the disease is given to the believer with a benevolent wisdom on the part of God. Moreover, some Muslim scholars have pointed out that sick people also remind other healthy people to give many thanks to God for their health, thereby channeling the whole community to the path of God. As such, what evolutionists claim as sub-optimalities are indeed essential parts of the divine plan, and they collectively function for the realization of the ultimate goal of creation. Thus, for Muslims, a disease is a gift of God with an evil face. As the Qur’an states, “it may well be that you dislike something while God has set in it much good” (Nisa 4:19). Again, a holistic view renders sub-optimality arguments unwarranted.

What these examples suggest is that most sub-optimality arguments are premature and assumptive. Proving a “poor design” argument requires more work than many evolutionists believe. Given our lack of comprehensive knowledge regarding the universe, it is safe to believe that we can never be sure whether something is ultimately sub-optimal. Nevertheless, this does not necessarily doom the study of optimality to a state of impasse. Although it is almost impossible to prove the theoretical optimality of things, we can assume tentative practical optimality in cases where we cannot suggest some practical means to improve on existing things. Thus, a practical test of optimality can be replacement of any purportedly sub-optimal thing in the universe with its artificial counterpart that is produced by human beings. If we can manage to replace any sub-optimal part with a better alternative without introducing new sub-optimalities elsewhere, then we might have a right to a tentative claim for sub-optimality. What is interesting is that all human attempts to improve on natural goods have failed so far. A prominent example to these failures is sugar substitutes. After the scientific discovery of the relationship between sugar consumption and certain health problems such as obesity and tooth decay, several scientists have advised that certain, if not all, people should refrain from or minimize sugar consumption. This resulted in a scientific interest in as well as a popular demand for sugar substitutes (or artificial sweeteners) that would give us the same sweet taste without sugar’s adverse effects. Surprisingly though, recent studies have demonstrated that sugar substitutes create more problems than they solve. Sugar-free sweeteners like aspartame and saccharin come with dozens of side effects, some of which are lethal.¹¹ Consequently, an increasing number of dietary experts advise us today to refrain from “diet” products, most of which include artificial sweeteners.¹² Thus, here we might be justified in claiming that natural sugar has practical optimality because it is proven to be superior to all other alternative sweeteners so far. Another prominent example is baby formulas. Despite all improvements in biochemistry, all baby formulas continue to come second after breast milk. Until human beings succeed in producing an infant formula that is overall more nutritious than breast milk and that is inexpensive enough to be produced in mass quantities, we are safe in saying that breast milk has practical optimality.

Finally, I should note that even if any sub-optimality does exist in the universe, it does not by itself provide any evidence for the absence of an all-powerful Creator. True, most believers believe in a God who is perfect in its self or essence and in its creation. Yet, this does not come to mean that any sub-optimality in the universe would necessarily negate the idea of God. From an Islamic point of view, for example, as everything in this life is part of a test, negligible sub-optimality might have also been purposefully included in God’s “design” as a test for human beings. If everything in the observed world was as perfect as each and every one of us would like it to be, there would be little room for disbelieving in God. However, the Qur’an states that this is not something God wished for human beings. Faith requires a struggle; and minimal sub-optimalities (if there are any) might be part of that struggle as well. If one in a thousand parts comes in seemingly sub-optimal character, it is not rational to conclude for the absence of intelligence or design.

Kaan Kerem has a PhD in Political science. He is freelance writer on philosophy and scientific thought.

1. Wordnet Online dictionary: http://dict.die.net/

2. Richard Dawkins, The Blind Watchmaker (New York: Norton, 1986), p. 91.

3. George Tsebelis, Nested Games: Rational Choice in Comparative Politics (University of California Press, 1991), pp: 6-7.

4. Dawkins, pp. 93-4.

5. Juan Ramon Martinez-Morales, Isabel Rodrigo, and Paola Bovolenta, “Eye Development: A View from the Retina Pigmented Epithelium.” BioEssays. 26:766-777, 2003.

6. Helga Kolb, “How the Retina Works,” American Scientist, 91:28–35, 2003. 7. Peter W.V. Gurney, Technical Journal, 13(1):37–44, 1999.

8. Massimo Pigliucci, “Design Yes, Intelligent No.” Skeptical Inquirer, September 2001.

9. Richard Swinburne, Is There a God? (Oxford University Press, 1996). Also see, Casey Luskin, Good Theology and Bad Design or Bad Theology and Good Design? http://www.ideacenter.org/contentmgr/showdetails.php/id/722

10. Said Nursi, The Flashes, trans. S. Vahide (Istanbul: Sozler Publications, 1996), pp: 26, 28, 334–336.

11. Janet Starr Hull, Sweet Poison (New Horizon Press, 1998). Visit author’s website www.sweetpoison.com for detailed information.

12. Michael F. Roizen and Mehmet Oz, You: The Owner’s Manual (Collins, 2005).