Seeing Vision’s Marvelous Process
[EDITOR’S NOTE: Dr. Ethan Wright holds an M.D. from the University of Missouri-Columbia. He completed his internship and residency at Texas A & M/ Scott & White Hospital. He has been practicing Ophthalmology in Arkansas since 2008 and is a Diplomate, American Board of Ophthalmology.]
The human eye is, perhaps, one of the most obvious examples of design which defies the theory of naturalistic, unintelligent evolution. The more we learn about the eye the more unreasonable it is to suggest that it would originate in some kind of natural way.
It is often said that a chain is only as strong as its weakest link. In many ways, vision is like a chain. It is a sequence of events where each step is dependent on every other complex component. If one single step is impaired, then vision as a whole suffers.
Consider a brief overview of the fascinating, seemingly instantaneous vision process, beginning with the first link of the chain—light rays traveling towards the eye—to the final step of the process where the brain interprets signals it receives.
When focusing on a distant object, light rays enter the eye in a parallel fashion. Objects that are closer emit light rays that are spreading (diverging). For eyes to fuse on an object—whether far, near, moving, or peripheral to where one is focusing—they must be coordinated perfectly through an extremely complex process. Multiple motor neurons throughout the brain communicate with each eye’s six muscles. For example, if one muscle pulls an eye to the right, the muscle that opposes it (designed to pull the eye to the left) must relax just the right amount to allow accurate fixation. When fully functional, this process appears to be instantaneous to the viewer. Both eyes must be precisely coordinated, or incapacitating double vision can result. Consider how quickly and smoothly one can read a line from this article and instantly jump to the next line below what was just read. These eye movements can be so powerful, they generate G-forces. In certain diseases, eye movement must be limited as these forces can negatively affect the eye’s health (i.e., hyphema).
As light reaches the eye, it encounters two lenses. The first and most powerful is the cornea. If the cornea has any abnormalities, such as scarring or being misshapen, there can be a significant effect on the clarity of vision. Even dryness of the corneal surface will commonly cause visual impairment. After the cornea, light travels through a fluid-filled chamber and then through the continually adjusting pupil, where it then reaches the native lens. The shape of the lens is constantly adjusted depending on if the light rays originate from a far object (parallel rays) or from a near object (diverging rays). Incidentally, when this lens loses its clarity and becomes hazy, it is called a cataract. If vision deteriorates enough to be problematic, the cataract is surgically replaced with an artificial lens, referred to as cataract surgery. Interestingly, the lens inverts and reverses images before they fall on the retina. The brain later compensates for this, so the images are perceived in the proper orientation.
After light leaves the lens, it travels to its final destination, the retina. The retina has some eight layers. Each layer must be fully functioning or vision is impaired. A single layer of pigmented support cells is just outside the retina (RPE). This layer appears to support the retina in at least six ways:
- Absorb light
- Maintain the anatomical shape under the retina
- Discard (phagocytosis) the spent rod and cone outer segments
- Metabolize the retinal fatty acids
- Form the essential barrier between blood and eye
- The repair and formation of scars
Again, if this single layer of cells (RPE) is not functioning, the overlying retina will suffer.
Traveling just beyond this pigment layer is the most densely vascular part of the human body, the choriocapillaris. This significant blood flow is believed to serve as a heat sink to remove thermal energy from the light absorption. Once light energy has reached the deepest layer of the retina (rods and cones), the energy converts to a neural impulse. Impulses are then carried to the brain by roughly 1.2 million fibers. All nerve fibers leave the eye through a small opening (optic disc) about 1.5 mm in diameter. This small opening can be damaged from elevated eye pressures, a disease known as glaucoma.
The visual impulses now leave each eye by means of its own optic nerve. Ultimately, these will both reach their destination in the back of the brain, the visual cortex. Not far after leaving the eye, the right and left optic nerves join briefly at a central location called the optic chiasm. Here, about 53% of these fibers cross to the opposite side of the brain, while the remaining 47% stay on the same side from which they started. Next, the fibers travel along the sides of the brain—splitting again, but vertically this time—until they reach the visual cortex (occipital lobe). Here, complex visual impulses are processed into meaningful information by which so many decisions are made. These nerves can sometimes be disrupted by strokes and tumors that occur along their path leaving permanent vision loss.
Our Creator’s design is evident in our vision. Every aspect of this chain of events must function precisely at all times for us to enjoy the vision with which God has blessed us. Macroevolution suggests each individual link of vision—each being entirely dependent on all the other links—would have to independently (and by chance) evolve without the influence from other yet-to-be-formed visual components. Yet, if one link is not present, the others provide no benefit. How could one part of the system develop where the other parts have not yet arisen?
The alleged evolution of vision is nothing more than an imaginary mirage, where people are “seeing” what they want to see rather than what is actually there. In truth, complex, functional design demands a Designer. Yes, the vision process has been fearfully and wonderfully made (Psalm 139:14)—a gift from the Creator.
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