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The Human Eye
Transcript of The Human Eye
The Eye and Its Function
Process of Seeing
The human eye is one of the most important organs in our entire body. The eye has a specific function, which is to receive light and to help us comprehend our surroundings. Information from the eye is put together like the pieces of a puzzle to create the picture of what we see. It has several parts, and is classified into three different tunics, or sections.
The outermost coat of the eye is called the fibrous tunic. This coat gives support and shape to the eye. This layer is divided into two parts: the cornea and the sclera. 5/6 of the fibrous tunic is made up of the sclera, while 1/6 is the cornea.
The vascular tunic is the middle layer of the eye. The vascular tunic controls the amount of light that enters the eye. This coat consists of the iris, pupil, lens, ciliary body, and the choroid.
The nervous tunic, the innermost tunic of the eye, contains the retina. The retina is made up of nerve cells and photoreceptor cells, cells that are stimulated by light, called rods and cones.
1. Light enters our eye through the cornea and pupil.
2. The lens focuses the light onto the retina.
3. Rods and cone cells turns this light energy into neural impulses.
4. The optic nerve sends these neural impulses to the brain.
5. The brain creates a logical picture of what is around us.
That's how we see!
Nearsighted people, who have trouble seeing things that are far away, have eyes that are too short, with the image placed too far behind the retina. Farsighted people, who have trouble seeing things that are close up, have eyes that are too long, with the image of the object placed too much in front of the retina. Concave glasses can correct nearsightedness, while convex glasses can correct farsightedness.
As you can see, the eye is one of the most significant sensory organs in our bodies. Although it appears to be small on the outside, it holds many things inside that are necessary for us to see.
•The cornea is the transparent “window” that is situated in the front of our eye. Light passes through the cornea as it enters our eye.
•The opaque white part of the eye is the sclera. The sclera is attached to the muscles that move the eye.
Iris and Pupil
The iris is the part of the eye that gives us our eye color. It houses the pupil. The pupil’s function is to regulate the amount of light coming into the eye. When more light is available, the pupil shrinks. When it is dark, the pupil opens up wide to let in as much light as possible.
Lens, Ciliary Body, and Choroid
Behind the iris is the lens, which is a transparent biconvex form that changes shape depending on the distance of the object seen. Its function is to focus light directly onto the retina. The ciliary body’s job is to adjust the shape of the lens through thin fibers that are connected to the lens. The choroid is behind the ciliary body. It carries blood vessels to and from the eye. Its dark melanin coloring prevents light from scattering in the eye.
Rods and Cones
Cornea and Sclera
The rods and cone cells convert the light energy that enters the eye into neural impulses. The rods cells are sensitive to dim light, not color. These cells are active in black-and-white vision, night vision, and motion detection. There are about 120,000,000 rod cells in each eye. Cones are sensitive to color. These cells are almost always active. There are only about 6,000,000 cone cells in each eye. The fovea is a small cavity in the eye where only cone cells are present, making the vision most intense here.
Nerve fibers in the retina connect to make the optic nerve, which sends the neural impulses to the brain to make a picture. When an image is projected onto the retina, it is upside-down. When the image is sent to our brain, the image is automatically flipped right side up.
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