The Amazingly Designed Human Body – Part 20
The Sense of Sight
Of the five basic senses, none is more miraculous than the sense of sight. For over a century, Bible believing creationists have used the complexity of the eye as proof that we were created by an infinitely intelligent designer God.
The two main organs involved in the sense of sight or vision are the eye and brain. The eye is considered by some to be the most complex and the most delicate of all the organs contained in the body.
The basic function of the eye is to capture light waves and convert them to electrical impulses which are sent to the brain via the optic nerve. The brain then takes those electrical impulses and interprets them as a visual image. It may sound simple, but when you really examine how it works, you will quickly see that vision is truly a miracle.
Most people think the eye consists of a lens, sclera, cornea, pupil, iris and retina. You may be surprised to know that there is so much more to it than that. Here is a list of the parts of the human eye:
- Anterior and Posterior Chambers or the space between the cornea and iris.
- Aqueous humor, a fluid that provides the cornea and lens with nutrients and oxygen.
- Canals of Schlemm, located around the iris, to facilitate the draining of aqueous fluid.
- Choroid, a layer of blood vessels between the sclera and retina.
- Ciliary body, the region where the aqueous humor is produced.
- Ciliary muscle, responsible for changing the shape of the lens for distance vision.
- Conjunctiva, a clear membrane in front of the eye and inner eyelids that produces mucous to lubricate the eye.
- Cornea, a dome-shaped surface that is the real optical system.
- Crystalline lens positioned behind the cornea, to maintain image-focus on the retina.
- Eyeballs in both eyes that offer binocular vision, by fusing images in the visual cortex.
- Eyelashes and eyebrows with protective hair.
- Eyelids to lubricate the eyes and keep them moist and clean.
- Eye sockets or cone-shaped cavities that protect the eye.
- Fovea, an indentation in the macula, responsible for highest visual acuity.
- Lacrimal gland or tear duct to prevents the cornea from becoming dehydrated.
- Lacrimal sac responsible for draining tears and debris from the eye.
- Iris, a ring of muscle fiber behind the cornea that responds to the brightness of surrounding light.
- Macula, a part of the retina responsible for central vision.
- Optic disk, a spot on the retina that creates the ‘blind’ spot.
- Optic nerve, a nerve fiber network that connects the eye to the brain.
- Six orbital muscles responsible for eye movement.
- Photoreceptor cells in the retina that send electrical signals to the brain.
- Pupil, responsible for enabling light to pass through.
- Retina, the eye film that converts light rays into electrical signals.
- Retinal pigment epithelium, a layer of cells between the retina and choroid that absorbs scattered and reflected light.
- Sclera, the white eye wall that uses internal fluid pressure to maintain eye shape.
- Visual axis, an imaginary line that facilitates the generation of a ‘fixation’ point.
- Vitreous cavity, the space between the lens and retina.
- Vitreous humor, a jelly like liquid that fills the eye.
- Zonules or string like fibers that hold the eye lens in position.
Now that you have been shocked by how many different parts there are to the eye, we will look at how they function to produce the wonderful world of sight.
For our purposes, we’re going to use a red ball as the object we are looking at. Light waves, whether from the sun or by artificial sources, strike ball. Most light waves are absorbed by the ball but the red light waves are reflected away from it. As the red light waves reach our eyes, they first meet the outer most surface of the eye known as the cornea.
The cornea acts like a lens cover protecting the inner parts of the eye and it also acts as the first lens. The cornea is composed of a layer of transparent epithelium cells. As the light waves pass through this transparent layer, they are bent towards the pupil.
The pupil is the dark opening in the eye. It is surrounded by the colorful iris. The iris contracts and dilates according to how bright the light waves are that are entering the eye. As the iris dilates, the pupil gets larger and lets in more light and when it contracts, the pupil becomes smaller, limiting the amount of light entering the eye. It operates very similar to the aperture on a camera lens.
The light waves from the red ball that manage to pass through the pupil then pass through the lens of the eye. The lens is biconvex in shape with the outer edge being some what flatter than the back side. The ciliary muscles attach to the lens and acts to pull and flatten it out to help the lens to focus on objects at various distances. The lens bends the light waves so that they focus on the retina in the back of the eye. However, the image that is focused on the retina is upside down and backwards.
Between the lens and the retina, the eye is filled with a fluid known as the aqueous humor. This fluid not only keeps the lens and cornea moist, but also plays a part in how the light waves travel through the eye to the retina.
I never realized the roll the aqueous humor played in vision until I had a retinal detachment about ten years ago. This experience also helped me realize just how opposite the image is focused on the retina compared to how the brain interprets it. When the section of retina detached, I noticed a large blurry area on the outer part of my vision in the one eye. When the eye doctor examined me, he told me that the detachment was near the nasal side of the eye, which is why I saw it on the outer area and not the inner. The lens of the eye reverses the image.
Part of the procedure to repair the retina required the eye surgeon to drain all of the aqueous humor fluid out of the eye. Then after he re-attached the retina, the eye takes about two weeks to replace the aqueous humor fluid. Without the fluid, everything was blurry out of that eye. As the fluid slowly filled the eye, I could see clearly through the fluid and blurry where there was no fluid. It was really strange to me as the fluid appeared in the upper part of my vision and the air bubble was at the bottom, again reinforcing the fact that the lens reverses the image.
After the light waves pass through the lens and aqueous humor, it reaches the retina. The retina is only about 0.5 mm thick and consists of three layers of nerve cells and two layers of nerve synapses. The light waves pass through these layers until they reach the layer of photoreceptor cells. The photoreceptor cells are made up of rod cells and cone cells. There are around seven million cone cells and ninety million rod cells in the human retina.
Many evolutionists try to argue that the human eye is not evidence of design because the retina is backwards. However, numerous tests have demonstrated that the retina was perfectly designed to function as it is. If the rod and cone cells faced outward instead of backward, the light would be so intense on them that they would soon be overloaded and cease to operate.
Rod cells are about one hundred times more sensitive to light than are cone cells. The highest concentration of rod cells is near the outer regions of the retina and is important in peripheral vision. The central focal area near the center of the retina have the fewest number of rod cells. Rod cells contain a single light sensitive pigment and are thought to have a very limited, if any, role in color vision.
Cone cells have three types of light sensitive pigments and are believed to have the main role of color vision. They are less sensitive to light, which is why the ability to distinguish color diminishes in lower light situations. The central focal area of the retina has the highest concentration of cone cells.
Each colored light wave has its own specific energy level or wave length. This energy is detected by the rod and cone cells and converted into nerve impulses that are then transmitted to the optic visual cortex region of the brain via the optic nerve.
If this was all there was to vision, you would be blind in a very short time. In order to keep the rods and cones working the eye has to continually move. To show you what I mean, stare at a single object without blinking for as long as you can. What happens? After a few moments, not only does the eye start to get dry and sore, but you will notice that your field of vision begins to shrink and eventually most of it goes dark. To avoid this from happening, the six orbital muscles that move the eye are constantly twitching, causing the eye to jump a fraction of an inch nearly a thousand times per second.
The eyes have their own cleaning and protection system. We have moveable eyelids that help protect the eyes from foreign objects and to help moisten the outer surface of the eye. The muscles controlling the eyelids can react extremely fast and instantly close when the brain detects a danger to them. Eyelashes also help protect foreign objects from reaching the surface of the eye. The lacrimal or tear ducts secrete a fluid that helps to not only keep the eyes moist but they also help wash out any particles of matter that do reach the surface of the eye.
Indeed the human eyes are a true testimony to our Creator God who wants us to see the world that He created for us and for His pleasure. He also wants us to see Him as Jesus said in Matthew 5:8:
Blessed are the pure in heart, for they shall see God.
Bible Doctrine for Older Children
Bible Doctrine for Older Children is a two volume series consisting of twenty chapter which contain simple explanations of all major biblical doctrines. Book A contains chapters 1-10 and Book B chapters 11-20. The explanations were written for children eleven years of age and older. This series contains more than 150 stories and illustrations to help explain the doctrinal concepts being taught.
These books were written for home, personal, or family reading; school Bible doctrine teaching; or church catechetical instruction.
Book A Chapters:
1. Introduction, Gods Revelation, The Bible
2. Gods Names, Gods Attributes, The Trinity
3. Gods Decree, Predestination
4. Gods Creation, Angels
5. Gods Providence
6. The Creation of Man, The Image of God, Mans Soul and Body, The Covenant of Works
7. The Fall of Man, Sin, Death
8. The Covenant of Grace
9. The Mediator, The Natures of Jesus Christ, The Names of Jesus Christ
10. The Offices of Jesus Christ, The States of Jesus Christ
Book B Chapters:
11. Doctrinal Standards, Creeds, The Five Points of Calvinism
12. Calling, Regeneration, Conversion
13. Faith, Types of Faith
14. Justification, Sanctification
16. The Church, The Church Offices, Church Government, Church Discipline
17. The Means of Grace, Gods Word, Gods Law and Gospel
18. Gods Sacraments, Holy Baptism
19. The Lords Supper
20. The Soul After Death, Christs Second Coming, The Resurrection of the Dead, The Final Judgment, Eternity