Physics of the Eyes

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Protections of the eye:

The human eye is one of the most important things to a person and thus has many forms of protection.

The eyelid protects the eye in three different ways: the eyelashes, the glands, and the movement of the eyelids.

The eyelashes are beneficial in keeping dust and debris out of the eye. Touching the lashes will trigger the reflexive blinking mechanism.

There are many different glands that are located in the eye. The Zeis gland is a gland that secretes oil. An infection in this gland results in a stye. A second gland, the Meibomian gland, are large oil secreting glands located in the lid of the eye and play a part in producing the oily outer layer of tears. This oily layer prevents the evaporation of tears. Also contributing to the make up of tears are the aqueous and mucous producing glands.

Eyelids protect the eye mainly by their rapid rate at which they cover the eye. Even though blinking interrupts the line of vision, the illusion of sight continues while the eye is briefly closed.

The Cornea:

The cornea is the front part of the eye and is a transparent tissue that lacks blood vessels and covers the iris and pupil. The cornea allows light rays to permeate and bends the light enough to allow for focusing of the eye.

The cornea contains five different layers:

* the epithelium

This is the outermost layer of the cornea. The cells of the layer offer a smooth surface that serves the tear layer well.

* Bowman's membrane

This is the main part of the cornea. It is a tough layer of transparent tissue that has no cells. It is made up of mostly collagen material.

* the stroma

This layer has other layers in it of tissue called lamellae which go through the e...

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...is focused on the retina. The image is actually seen on the retina upside down, and is reversed when it is sent to the brain. Recall that the left side of the brain controls the right side of the body, and in remembering this, the fact that the left half of the visual field in each eye is sent to the right half of the brain.

Although an eye is likened to a camera, "[t]he one major difference is that the focus of the eye is altered by changing the focal length (or power, P=1/f) of the lens, rather than by changing the distance between the lens and the retina." (www.dur.ac.uk/r.g.bower/OpticsI/optlec/node34.html)

Works Cited:

Cassel, Gary, et al. The Eye Book: A Complete Guide to Eye Disorders and Health. The John Hopkins University Press: Baltimore & London. 1998. (pp. 3-15)

D'Alonzo, Dr. T.L. Your Eyes! Avanti Publishing: Pennsylvania. 1991. (pp. 15-54)

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