The Human Eye

Topics: Eye, Superior oblique muscle, Cranial nerves Pages: 7 (2687 words) Published: May 6, 2010
The eye is a rather small part of the body that makes up seventy percent of the humans total sensory ability. That is why we chose to describe the eye. Each part of the eye works together as a whole. Within and outside of the eye there are many working parts functioning around the clock.. The cornea is a very important part of the eye, but you can hardly see it because it's made of clear tissue. Like glass, the cornea gives your eye a window in which to view the world. The a cornea is a transparent tissue covering the front of the eye. The cornea covers both the pupil and he iris eye, and it is partially responsible to focus light. The cornea is part of the external structure of the eyeball. The external layer of the eyeball is formed by the cornea, and the sclera. The cornea is a dome-shaped structure. The cornea does not have any blood vessels that is why it appears clear. The cornea does have nerves. The cornea is the first and most powerful lens in the eye's optical system. The cornea is the first part of the eye to focus. When a ray of light hits the eye, the cornea is the first structure the light encounters. Then the light rays travel through your eye through a hole called the pupil. As light rays from an object enter your eye, they are bent inward by the cornea and lens. Light rays are focused through the transparent cornea and lens. Light rays focused by the cornea and lens produce an image on the retina that is upside down. The cornea is made up of five layers: the epithelium, Bowman’s layer, the stroma, Descement’s membrane, and the endothelium. The cornea obtains oxygen through absorption from the tear film layer, and from the aqueous humor. The tears that flow over the cornea help to keep it nourished and moist. {draw:frame}

The anterior chamber lies between the iris and the back surface of the cornea. There are three chambers of fluid in the eye. The anterior chamber, which is between the cornea and iris. The posterior chamber, which is between the iris and lens. And, the vitreous chamber, which is between the lens and the retina. The fluid filled substance is called the aqueous humor. It is a clear fluid that fills the anterior chamber and the posterior chamber of the anterior cavity of the eye. The aqueous humor bathes the lens and gives nourishment to the lens. The aqueous humor is produced by the ciliary body. {draw:frame}

{draw:frame} The colored part of the eye is called the iris. It controls light levels inside the eye similar to the hole on a camera. The round opening in the center of the iris is called the pupil). The iris is embedded with tiny muscles that dilate (widen) and constrict (narrow) the pupil size. The sphincter muscle lies around the very edge of the pupil. In bright light, the sphincter contracts, causing the pupil to constrict. The dilator muscle runs radically through the iris, like spokes on a wheel. This muscle dilates the eye in dim lighting. The iris is flat and divides the front of the eye (anterior chamber) from the back of the eye (posterior chamber). Its color comes from microscopic pigment cells called melanin. The color, texture, and patterns of each person's iris are as unique as a fingerprint. The pupil is the black circle in the center of the iris. But, the pupil is really a clear opening. The pupil appears black because the light which the pupil allows to enter the eye is absorbed on the retina and does not exit the eye. Light enters the eye through the cornea; it then travels through the opening called the pupil. Light then enters the eye's lens. The pupil changes size in order to adapt to the quantity of light rays that reach it. The pupils constrict in response to increased light, this makes your pupils smaller. When the pupils are smaller, it allows in as little light as possible. The pupil dilates in response to decreased light, this makes your pupils larger. When the pupils are larger, it allows in as much light as...
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