Human anatomy > Sensory organs > Eyeball

The eyes are one of the most important parts of the human body. Without it, learning can be very difficult. Because people primarily learn things by seeing, without the eyes, it will be very difficult to accomplish tasks. This makes it more challenging for people with visual problems to enhance their other senses just to compensate for the loss of one. To understand how the eyes help in perceiving the things around you, here are some parts of the eyes and their functions. 



The eye is comprises of three coats: the fibrous tunic, the vascular and the nervous tunic. The fibrous tunic consists of the sclera and the cornea; the vascular has the choroid, ciliary body and the iris; and the nervous has the retina. Each of these coats help in keeping the functions of the eyes. 


The sclera is the outmost covering of the eye and is found mostly on the posterior part of the eyeball. Dense collagenous connective tissue makes the bulk of the coat. It provides a point of attachment for the muscles, serves as a protector for the interior parts of the eye and keeps the shape of your eyeball. In the anterior part, the sclera becomes the cornea. The cornea has no blood vessels and permits the entry of light to the eye. Because the cornea is easy to remove and has no blood vessels, it is the first organ transplanted. Since it is less immunologically active, success of transplantation is high. 


The iris is the colored part of the eye. It is responsible for the natural colors of your eye. If you have brown to black iris, it means more melanin is in your eyes. The melanin protects your eyes from too much light. When the light enters the pupil, the iris functions the same way like the iris diaphragm in the microscope. It regulates the amount of light entering the eyes. It accomplishes the task with the aid of the smooth muscles sphincter pupillae and the dilator pupillae. 


The retina is part of the nervous tunic. It contains the sensory receptors housing the millions of photoreceptors, the rods and the cones. It is in the retina where an image is formed. Upon inspection, you will see two important parts, the macula lutea and the fovea centralis. The macula lutea focuses the light, whereas the fovea centralis is the area of greatest visual acuity. 
With a simple understanding of the different parts of the eyeball, you can better appreciate how each part relates to another to give you the best image possible. 

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