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Eye Structure introduction
The entire structure of the eye is housed inside a bony socket called the orbit. The orbit is pear shaped and is in essence the container for the eye. The total structure of the eyeball and its socket is quite complex and includes the muscles, nerves, blood vessels, eye tissues and aqueous humor.
The human eyeball is constructed of the following elements:
The sclera surrounds the entire eyeball. It can be described as a tough white outer layer that encloses the other components. The sclera is thick connective tissue. The sclera in turn is covered by a mucous membrane called the conjunctiva covers the front of the eyeball.
The conjunctiva is a thin mucous membrane that extends to the edge of the cornea but that also acts as a cushioned lining for the inside of the eyelids.
The cornea is a transparent, extremely sensitive, clear dome of tissue on the anterior surface of the eye. The cornea serves as a protective covering for the black hole known as the pupil. The cornea also has a refractive surface that helps to focus light on the retina, which is situated at the posterior of the eye.
The iris is a layer of fine muscles that surrounds the pupil. It is the pigmented part of the eye. The pupil is actually a hole in the iris through which light passes. Like as shutter in a camera the tiny muscles in the pupil control the amount of light entering the eye. The pupil dilates when it is bright or to let in more light and contracts when there is too much light.
The lens is located behind the iris. It is a small clear piece of protein rich tissue that is dryer than other tissues in your body because they are only 65% water. and is relatively dry containing only 65% water. The purpose of the lens is to focus light inside the eye and onto the retina. It does this by using small muscles in the iris called the ciliary muscles, which thicken and thin depending on where they want to focus. The lens is fixed to the ciliary muscles with fine thread like structures.
The retina is a thin see-through membrane at the back of the eye. It is like a movie screen on which images are projected upside down. The brain makes sense of the image and turns it right sided up. It is the part of the eye that actually sees. Millions of light-sensitive cells and photoreceptors are located in the retina.
The largest cluster of photosensitive cells are located in the part of the retina known as the macula. The macula assists in creating detailed images. The proper functioning of the retina is critical to the ability to focus.
Each photoreceptor in the eye is attached to a nerves that when clustered together become the optic nerve. The photoreceptors transform incoming light beams into electrical impulses and the optic nerves relay electrical impulses to the brain.
There are two types of photoreceptors in the retina. These are called cones and rods. Cones help produce clear, sharp color images. The rods are used more for peripheral vision and night vision. The cones do the majority of seeing for you in the day and the rods take over at night
Rods are mainly found in the peripheral regions of the retina. There are more of them then cones but they cannot perceive color. Rods can only detect shades of grey, which is why when it gets dark w is unable to see color.
The Interior of the Eyeball
Two distinct chambers make up the inside of the eyeball. Both are filled with fluid. The anterior (front) chamber extends from the inside of the cornea to the front part of the lens and is filled with a fluid called the aqueous humor. The posterior (rear) chamber extends from the back of the lens to the retina. It is filled with vitreous humor. These fluids create tension and form so that the eyeball can retain its round shape.
The anterior chamber is divided into two further sections. The front section extends from the cornea to the iris and the rear section extends from the iris to the lens. The aqueous humor is produced in the back part of this sub chamber section and is dispersed through the pupil into the front section. The fluid then drains out of the eye to moisturize the surface of the eye and keep it intact.