The cyclops hails from Greek mythology and first appears in Homer’s Odyssey, and it was a giant one eyed humanoid monster with a taste for humans. Manako is a monoeye, or the cyclops of the Everyday Life of Monster Girls, and much cuter than the cyclops of Greek mythology. Interestingly enough, unlike zombies, there are examples of real world cyclops, or one-eyed versions of animals that would normally have two eyes.
The condition is known at cyclopia, and it is an uncommon birth defect that occurs in about 1 in every 16,000 animals. It is also thought to be involved in about 1 in 200 miscarriages (no pictures because I don’t want anyone to lose their lunch). The reason that it is occasionally seen in live animals as compared to live humans is due to the degree of brain malformation that occurs and how it impacts the rest of the developing baby.
The human nervous system begins to form during the first few weeks of development, and the brain is formed from three structures: the hindbrain, midbrain, and forebrain.
The forebrain eventually develops into the cerebrum, or the top half of the brain, which is where conscious thought, sensory information processing, and muscle control are located, just to name a few. Even those of you with limited knowledge of the brain have probably heard the phrase left brained, or right brained, and this is so because the human brain is split in two.
In cyclopia, the forebrain does not divide into two halves, which means that there is only one lobe of the brain instead of two. This is, of course, very damaging to the developing organism for a multitude of reasons. The two main ones are that half of the brain is essentially missing, and the nervous system impacts the skeletal system that develops around it. Now I already can hear the questions coming: “but teacher wouldn’t the brain be the same size as a normal brain?”
Yes, the brain of an individual with cyclopia would be the same size as a normal brain, but it is essentially missing half of the parts. This is so because the right and left sides of the brain specialize in different functions, and half of them would be missing if one side of the brain did not develop. This is also why only one eye develops, as one eye develops from each side of the brain. In animals with less complex brains cyclopia is less damaging and that is why you can sometimes find it in animals, but in humans the damage is so severe that the fetus cannot completely develop and a miscarriage occurs.
If we assume that our cyclops Manako has some sort of special monster girl physiology that allows her to function with a one lobed cerebrum, there is one more issue to be discussed, and that is depth perception. Depth perception is the ability to visually determine just how far away a particular object is, or seeing in 3 dimensions. It is possible to have depth perception in both monocular (one eye) and binocular (two eyes) systems, but binocular systems are more effective.
In single eye or monocular vision, how far away an object is, is determined using a variety of factors including, motion, perspective, texture gradients, accommodation, and the relative size of objects. Motion helps to provide depth perception because, the farther away an object is from you the slower it will appear to move across the background. Imagine looking up at a plane flying overhead; the plane appears to slowly move across the sky even when it is going hundreds of miles an hour, while a baseball thrown just over your head will appear to move much faster, even when it is going significantly slower. Another way that motion provides depth perception is that as an object moves closer or further away from the individual, its relative size changes. Going back to baseball, the ball appears bigger as it moves closer towards you and smaller as it moves away from you. The same is true even without motion- the closer the object is to you, the larger it appears, and the further away it is from you, the smaller it appears. An example would be gravel: from the distance it can appear smooth, but close up it can look quite rough.
All of the methods used in monocular systems to determine the distance of an object will be present in binocular (two eye) systems. However, what makes binocular systems much better at determining depth perception is the use of parallax. Parallax is the change in location of an object when viewed from two different locations. Math can then be used to determine the distance of the object from the viewpoints.
As it turns out, the human brain can do this using our eyes. Now you might be thinking “but I’m not standing in two different places when I look at something, and yet I know relatively how far away the object is.” This is, of course true, but humans have two eyes, and each eye will view an object differently. If you don’t believe me, I want you to try something at home. Find two separate objects that are relatively close together and some distance away from you. Cover the eye that is on the side of the object that is further away and turn your head until the object in the distance disappears. Now uncover your eye and you should see the object jump back into your field of view. So even though our eyes are closer together on our head, they are far enough apart to count as different viewpoints. I have also illustrated this in the diagram below.
One last item to note is that the greater the overlap in the field of vision between the eyes, the greater the area of depth perception. This is why predators typically have eyes that are set closer together on the head, so that they are better able to judge the distance of their prey.
So yes, an individual with one eye will have some degree of depth perception, but it will not be as good as an individual with two eyes. Studies have also shown that individuals with only one eye tend to have more trouble with balance issues outside of their depth perception problems. Everyday Life with Monster Girls, plays this straight as Manako is rather clumsy at times.