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The Function Of The Human Eye.

1156 words - 5 pages

The Function of the Human EyeInarguably, the human eye is one of the most complex human organs in the body. The eye aids in almost every activity that people participate in (excluding pin the tail on the donkey). Scientists can only guess at the probability in evolution of the eye being formed; there are so many variables that a close number would be incalculable. The eye is an extraordinary part of the human body; most people agree that is the most important sensory organ. The eye sends messages to the brain via optic verves, not unlike information through a computer. To understand how the eye works we must first see what the eye is made up of. The eye has various parts with various functions.The human eye is capable of forming images of objects miles away, detecting a countless variety of colors and responding to small amounts of light. The globe of the human eye consists of a tough, white outer layer of connective tissue called the sclera and a thin, inner layer called the choroid. A layer of epithelial cells forms a mucous membrane called the conjunctiva that covers the outer surface of the sclera and helps keep the eye moist. At the front of the eye, the sclera is then called the cornea, which lets light into the eye and acts as a fixed lens. The anterior choroid makes up the iris (the colored part of the eye. The iris regulates the amount of light entering the pupil by changing the size of the hole in the middle. Within the choroid, the retina forms the innermost layer of the eyeball and contains the photoreceptor cells. Information from the photoreceptors leaves the eye at the optic disc, where the optic nerve attaches to the eye.The lens and ciliary body make two cavities in the frontal region. The ciliary body produces a watery discharge. The other cavity covers most of the internal eye. These discharges help to bring pictures into focus. The lens is a transparent protein disc that focuses an image onto the retina. Humans focus by changing the shape of the lens. When viewing a distant object, the lens is flat. When focusing on a close object, the lens becomes almost perfectly round.The human retina contains about 125 million rod cells and 6 million cone cells, two types of photoreceptors named for their shapes. They account for 70% of all sensory receptors in the body, a fact that underscores the importance of the eyes and visual information in how humans perceive their environment.Rods and cones have different functions in vision. Rods are more sensitive to light but do not distinguish colors; they enable us to see at night, but only in black and white. Because it takes more light to stimulate cones, cones do not function in night vision. Cones can distinguish colors in daylight. In the human eye, rods are found in greatest density at the peripheral regions of the retina and are conversely absent from the center of the visual field.When the lens focuses a light image onto the retina, each rod cell or cone cell has an outer segment with...

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