How the Eye Sees Upside Down
The process of being able to see is more complicated than you might imagine. It takes more than just lifting an eyelid to be able to take in everything visually. The eye is made up of many parts that play important roles in producing images. An interesting fact about the human eye is that it initially flips images upside down, much like a camera does when taking pictures.
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Structure of the Eye
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Light enters the eye through the cornea, the dome located at the front of the eye. The light then passes through the pupil, which is the dark circle in the middle of the iris, the colored portion of the eye. The crystalline lens is located right behind the iris and cornea. The image passes through this lens and appears on the back of the lens upside down and backwards.
Role of Light
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When light travels from one substance to another, it changes speed and direction. This is called refraction, and it explains why something appears to be shifted to a different spot when under water. When light travels through the eye, it bends, because eyes are made of different substances than the air.
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Light Bends
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Due to the nature of light and the structure of the human eye, light is bent and converged when it goes through the cornea, and then further by the crystalline lens. By the time it reaches a single point (nodule point) in the back of the lens to form a picture, the light has been inverted and reversed, making objects appear upside down and backwards.
Role of the Brain
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Once the light has converged to a single point, it travels through the vitreous humor, a clear gel-like substance which makes up about 80 percent of the eye, and focuses on the retina, which could be considered the "film" if the eye were a camera. The light then changes to electrical impulses that travel through the optic nerve to the occipital cortex located at the back of the brain where the image is corrected, allowing you to see right side up.
Misconceptions
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Many think the eyes are what allows humans and other animals to see objects. While the eye plays a significant role in the visual process, it is merely a receptor for light. The part of the body that actually allows you to see things is the brain. Without the brain, eyes would be useless. Of course without eyes, the brain would have no light to work with, making eyes extremely crucial in the visual process.
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References
- Photo Credit eye image by Stanisa Martinovic from Fotolia.com
