Desmond E. Bing
Professor Kerr
English 101-H4
Eye to Eye
It is generally accepted that cats and dogs are colorblind due to a sensitivity they have to specific colors. Snakes have employment of two sets of “eyes” so to speak: one set during the day, by which vision is carried out solely through the movement of an object and the other set for night, which utilizes infrared heat signals to help snakes identify their surroundings. Most insects have compound eyes, made up of hundreds or even thousands of tiny lenses placed together in a honeycomb pattern creating a jigsaw or puzzle like scope to their vision (Vision and Health Resources). Vision and Health Resources, an online directory that aids one in the finding of a local eye doctor and provides information and statistics on the eyes of humans and animals, states that how one views their world can be determined by a multitude of factors. Not all animals, be they big or small, see the world as humans do. For many animals, the world is seen in fuzzy shades of gray or washed out “pale” colors. On the other hand, for some, living in perpetual darkness has given way to colors beyond our wildest dreams; shades that cannot be seen by humans on the color spectrum. Others can use binocular vision to spot prey thousands of feet away (Vision and Health Resources). The human and animal eye can be observed in order to find the differences and similarities between the placement of the eyes, the depth of the visual spectrum, and the diseases that can occur to the eyes.
Every animal species, including humans, has evolved eye placement that best ensures its survival. The location of the eyes on an animal's body determines how that particular animal receives visual information. Most animals have eyes that are either on the front of the head, like humans, or the side of the head, but in some rare instances such as with Crocodiles and Alligators, the eyes can often appear on the top of an animal’s head. Eyes in the front of the head provide binocular vision and excellent depth perception, which is why humans have the capability of seeing intricate patterns and abstract colors (Human vs. Animal Eye). Most predators, as with the example of tigers, wolves, and hawks, have eyes in the front of the head that allow them to stalk and chase fleeing prey. Although this evolutionary trait can create excellent hunters, there are strong disadvantages that accompany binocular vision such as large blind spots and limited peripheral vision, which make it easy for prey to hide. Conversely, an animal with eyes on the side of its head has a wide range of vision. For example, deer, rabbits, and many other herbivorous prey animals have eyes on the side of their heads, allowing them to see predators at any angel while grazing. The only drawback to this attribute is that eyes on the side of the head can often create a blind spot directly in front of the animal; but a strong sense of smell helps to overcome this handicap (Human vs. Animal Eye).
The sun emits energy at different wavelengths, and visible light comprises just a tiny part of the solar color spectrum. Visible light is capable of penetrating the earth’s surface quite easily and is actually part of the electro-magnetic spectrum, which is why every animal on earth sees at a slightly different spectrum (Art and Science of Vision). Color Wavelengths can be categorized by long or short. At the long end, some fish and butterflies see a little into the infrared, which gives them extra visual sensations at dawn and dusk. Humans can see a sufficiently powerful infrared source, as vision pioneer George Wald discovered while developing infrared-based viewing devices for the US Board of Army Engineers during the Second World War, but only with the use of special equipment because the human eye is not normally able to see infrared wavelengths (Art and Science of Vision). The short end is dominated by ultraviolet rays. While ultraviolet rays pose a threat to most mammals that are active during the day, humans have evolved a unique pigment in the lens that absorbs ultraviolet rays almost completely. Squirrels have also developed an anecdote to ultraviolet rays. The lens of the squirrel has a yellowish tint to it creating a barrier for the eye against the harmful rays (Art and Vision of Science).
The eyes are one of the smallest and most complex systems working in the human body, which makes them prone to many types of diseases that can affect their productivity. Although it is only about the size of a pimple, a sty can be extremely annoying and painful. This inflamed or infected swelling can be the result of an infected follicle or a blocked gland in the eyelid. Sties are sometimes, but not always, related to blepharitis, which can only occur in the human eye (Vision and Health Resources). Blepharitis is an inflammation of the edges of the eyelids, causing redness and thickening. The disease is common, especially in children, and often affects the upper and lower eyelids of both eyes. There are two types: ulcerous and nonulcerous. Infection of eyelash follicles and oil glands cause ulcerous blepharitis. The nonulcerous variety, which is more common, can be caused by an allergy or seborrheic dermatitis, which is an inflammatory scaling of the scalp, eyebrows, or ears (Discovery Health). A common disease that attacks primarily domesticated animals is having a detached retina. Normally, the retina is firmly attached to the choroid, an underlying layer of tissue that is rich in blood vessels. If sufficient blood or other fluid collects between the retina and the choroid, the retina can become partially or totally detached (Vision Health Resources). A disease that can occur in both animal and human eyes is known as Conjunctivitis. Conjunctivitis, also called pinkeye, is an inflammation of the conjunctiva, a delicate membrane that lines the inner surface of the eyelid and covers the exposed surface of the eye. Bacteria and viruses are the usual causes of conjunctivitis. Allergies, chemicals, dust, smoke, exposure to chlorine in swimming pools, and foreign objects that irritate the conjunctiva may also lead to this condition (Discovery Health).
Animals develop behavior to respond to the information that is being given to them in a specific instance. Unlike humans, they tend to focus on the act of seeing rather than what is being viewed in order to sustain survival. Humans enjoy the magnificence of consciousness. We can appreciate seeing for its own sake and tend to assume that the eye is simply a window on the world (Art and Science of Vision). Both human and animal eyes, in terms of their placement, depth of the visual spectrum, and proneness to disease, paint a picture that has yet to be completed. We have no inkling of the future holds for our eyes; will humans always be able to filter harmful rays? Will certain animals ever be able to see colors as we do? Moreover, what we will be able to see if our eyes develop the ability to view more than we ever dreamed possible? Our eyes, human and animal alike, give us the possibility of creating a world without boundaries or limits.
Works Cited
Ings, Simon. A Natural History of Seeing: The Art and Science of Vision. W.W.
Norton & Company. New York , NY London , England
Eyesandvision.com. Vision Health Resources. Web, October 3, 2010 . Vision Health
2006- 2010 http://www.eyes-and-vision.com/how-animals-see-the-world.html
eHow. Human vs. Animal Eye Location. Web, October 4, 2010 . eHow, Inc. 1999-2010
http://www.ehow.com/facts_5732079_human-vs_-animal-eye-location.html
Discovery Health. Eye Care. Web, October 2, 2010 . Discovery Health, Inc. 2010
http://health.howstuffworks.com/wellness/beauty-hygiene/how-to-care-for-your-eyes4.htm
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