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The Human Eye Essay

The Function Of The Human Eye

The Function of the Human Eye

Inarguably, 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...

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The Human Eye Essay

The Eye is the organ of sight. Eyes enable people to perform daily tasks and to learn about the world that surrounds them. Sight, or vision, is a rapidly occurring process that involves continuous interaction between the eye, the nervous system, and the brain. When someone looks at an object, what he/she is really seeing is the light that the object reflects, or gives off.

This reflected light passes through the lens and falls on to the retina of the eye. Here, the light induces nerve impulses that travel through the optic nerve to the brain, where it makes an image of the object, and then that image is passed on to muscles and glands.The eye is well protected. It lies within a bony socket of the skull. The eyelids guard it in front. They blink an average of once every six seconds. This washes the eye with the salty secretion from the tear, or lachrymal, glands.

Each tear gland is about the size and shape of an almond. These glands are located behind the upper eyelid at the outer corner of the eye. After passing over the eye, the liquid from the gland is drained into the nose through the tear duct at the inner corner of the eye.Heavy laughter or crying causes muscles in the upper eyelid to squeeze the lachrymal gland. This produces tears that flow too fast to be drained away. The eyelashes catch many flying particles that otherwise would enter the eye.

As further protection, the eyelids automatically close when an object suddenly moves close to the eye.Parts Of the EyeThe eye is made of 3 coats, or tunics. The outermost coat consists of the cornea and the sclera. The middle coat contains the main blood supply to the eye and consists of the choroid, the ciliary body, and the Iris. The innermost layer is the retina.Cornea and ScleraThe Sclera, or the white of the eye, is composed of tough fibrous tissue. On the exposed area of the eye the scleral surface is covered with a mucous membrane called the conjunctiva.

This protects the eye from becoming dry.The Cornea, a part of the sclera, is the transparent window of the eye through which light passes. The focusing of the light begins in the cornea.Behind the Cornea is a watery fluid called the aqueous humor. This fluid fills a curved, crescent shaped space, thick in the center and thinner toward the edges. The cornea and the aqueous humor together make an outer lens that refracts, or bends, light and directs it toward the center of the eye.IrisBehind the aqueous humor is a colored ring called the iris. The color of the iris is inherited and does not affect vision.

The iris is like a muscular curtain that opens and closes. It controls the amount of light entering the eye through the pupil, an opening in the iris. The pupil looks like a black spot. Light from everything a person sees must go through the pupil. When more or less light is needed to see better, the pupil becomes larger or smaller through the movement of the muscle in the iris.

The aqueous humor flows through the pupil into a...

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