Basic Structures of the Eye

Here is a set of notes I took about the basic structure of the eye. Enjoy! (The image is a focused shot of my right eye.

Visual process/ basic optical system - When a person looks at an object, the light rays that will reflect off the object enter the eye through the front and into the back of the eye. During the process, the light rays are bent and produce an upside-down image onto the retina. This image is then turned into electric impulses that travel to the brain where the image is translated and the object is then able to be perceived as upright. Light enters the globe through the cornea to the lens which also helps to bend the light and the light then travels through the vitreous to the retina where the information is changed into the electrical impulses and sent to the brain by the optic nerve.

Globe- the structures and membranes that together comprise the solid round shaped eyeball.

Cornea- the outermost front part of the globe. It is a thin, tough, crystal clear membrane that is sometimes called the window of the eye. It is transparent due to a lack of blood vessels which distinguishes it from other tissues as the cornea receives its nourishment from the tear film that covers its surface and a specialized fluid that flows beneath it. It provides 2/3 of the total refractive power of the eye and is the chief refracting tissue. There are five layers to the cornea body

-------- Corneal epithelium - first line of defense against injury and infection.
-------- Bowman's membrane - this membrane serves as the anchor to the epithelium layer.
-------- Corneal stroma - the main body of the cornea and contributes rigidity to the cornea. 90% of corneal thickness
-------- Descemet's membrane - provide some rigidity to the corneal body; a thin layer of collagen and elastic fibers
-------- Corneal endothelium - has cells that service pumps to maintain a proper fluid balance in the cornea and also help provide nutrients to the whole. It is a layer of delicate cells that cannot regenerate.

Sclera - the white tissue surrounding the cornea which is a strong fibrous outer layer that helps protect the intraocular parts and structures. So the white of the eye is actually bulbar conjunctiva which is translucent over the tissue of the sclera. Covers over 80% of the eyeball including whole of the rear.

Limbus - the juncture between the sclera and the cornea. The bulbar conjunctiva terminates here.

Anterior chamber - the area between the cornea and the iris. It is a small compartment filled with a fluid called aqueous humor that helps nourish the cornea. It is deepest at the center.

Iris - this structure is a colored diaphragm of tissue that is stretched across the back of the anterior chamber. In essence, creating the chamber between itself in the cornea. Using both a dilator muscle and a sphincter muscle, the iris can make the hole in the center pupil larger or smaller to control the amount of light that can be captured by the inside of the eye. It controls the pupil by involuntary reflex.

7. Pupil - this is not an actual structure; simply a name for the absence of structure or the hole in the center of the iris. The iris controls the size of the pupil and aqueous humor flows through it into the anterior chamber. It appears black because there is no light in the back of the eye to shine through to the front.

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