Most people will initially visualize an eye as the organ that allows a living being to see. The human eye, however, is a complex organ comprised of many parts that work together to control vision. Healthy eyes will serve you well until you die, and ophthalmologists--eye doctors--recommend having your eyes checked every two years to ensure their continued health and catch minor problems before they become major.
Parts
The sclera is the white part of the eye, which covers and protects almost the entire eyeball. The iris is the colored part of your eye, and the pupil is the black spot at the center of the iris. The cornea is a clear covering that protects the front of the iris and pupil. Directly behind the iris and pupil is the lens. The back of the eye is the retina, and the optic nerve is the nerve that connects the eye to the brain.
How It Works
When looking at an object, an image enters the eye through the pupil. In a functional eye, that image becomes inverted when it reaches the lens, and an upside-down version of the object is projected onto the retina. The retina transmits this upside-down image to the optical nerve; the optical nerve then conveys that image to the brain, where it is flipped over again, allowing you to properly see what is in front of you.
Vision Problems
Blurred vision comes in many forms, many of which can occur at any age. Nearsightedness, medically referred to as myopia, is the ability to see what is close to you, making everything far away appear blurry. Farsightedness, medically called hyperopia, is just the opposite, in which everything far away is clear and everything near you is blurry. Astigmatism is another cause of blurred vision and may be caused by an irregularly shaped cornea or irregularly shaped lens.
Maladies
Cataracts, an age-related condition in which your lenses become cloudy, is one of the most common eye-related diseases. Glaucoma is is a condition in which your optic nerve sustains damage because there is too much pressure in your eye. Conjunctivitis, better known as pinkeye, is fairly common in children, though adults who are exposed to it may get it as well. Conjunctivitis may be caused by allergies, eye drops, eye ointments or contact lens products, but it is most commonly caued by bacterial or viral infections.
Other Eyes
The calm center of a hurricane is referred to as an eye, and the hole in a sewing needle is also called an eye. The phrase "mind's eye" refers to an image you are visualizing. The Third Eye, in mysticism and occultism, is more of a psychic eye, an inner vision associated with your brain's Pineal Gland that allows you to see beyond the physical image in front of you.
