A relatively small organ in the human body, the eye is a passageway to understanding and emotion. Not only does the eye allow us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or give off, but it also enables us to see and interpret unspoken words and unexplainable environments.
The eye is complex — able to see in dim light or bright light, but cannot see objects when light is absent. It acts as a conductor as it changes light rays into electrical signals and transmits them to the brain, which interprets these electrical signals as visual images.
Protected by the cone-shaped cavity in the skull called the orbit or socket, the eye measures approximately one inch in diameter. The orbit is surrounded by layers of soft, fatty tissue which protect the eye and enable it to turn easily through the use of six muscles. Some of the more important parts of the human eye are the cornea, lens, iris, pupil, retina, sclera, the vitreous body, and the optic nerve.
The cornea has many of the same characteristics as a pane of glass: focusing power and a protection factor to the inner components.
The cornea provides most of the focusing power when light enters your eye -- the more rounded the shape, the clearer the image (see Common Focusing Errors). There are five layers of tissue to the cornea. The epithelium (the outer layer) is the eye's protective layer. This layer has the ability to heal quite quickly from superficial injuries due to highly regenerative cells that have the ability to grow back within three days. Most of the inner layers provide strength to the eye.
Like the lens of a camera, the eye lens's primary function is to provide fine-tuning for focusing and reading. The lens performs this function by altering its shape. Unfortunately, age can deteriorate the effectiveness of the lens. Presbyopia is a condition where the lens becomes more and more inefficient when trying to fine-tune an object. This occurs starting around the age of 40-50. Plus, many people over the age of 60 experience cataracts, which occur when the lens becomes cloudy and hard, preventing light from entering the eye.
Do you have blue eyes or brown eyes? This is determined by looking at the iris, or the colored part of the eyes. The primary function of the iris is to control the size of the pupil by contracting or expanding the muscles of the iris.
The pupil is the black circle that you see in the center of people's eyes. This works like the shutter of a camera, controlling the amount of light entering the eye. When you are in a bright environment, the pupil becomes smaller to allow less light through. When it is dark, the pupil expands to allow more light to reach the back of the eye.
The fine nerve tissue which lines the inside wall of the eyes and acts like the film in a camera is called the retina. The retina transmits images, in the form of electrical signals, to the brain.
Although unseen, this clear gel-like substance is located inside the eye's cavity, providing the eye's spherical shape. If you see small dots that dance across your visual field, it could be that the vitreous has developed small clumps known as "floaters." Interestingly, these are more common in nearsighted people than in the rest of the population.
The optic nerve is located at the back of the eye. It combines the signals created by the retina and carries them to the brain where they are interpreted as images.