The eye is one of the most extraordinary and complex parts of the body. It also has great symbolic meaning. We have all heard the expression, "The eyes are the window to the soul." Of all the parts of the body, they are always ready. When we wake in the morning, the muscles of our bodies need time to get moving. Not so the eye muscles. The eye is ready for action all the time.

How the eye works

Light enters the eye through a thin film of tears lubricating the cornea, which is the "front window" of the eye, and helps focus the light. On the other side of the cornea is the "aqueous humor," a clear watery fluid that moves in the front part of the eye and maintains a constant pressure. Next the light passes through the pupil, a small opening in the colored part of the eye, which is called the iris. The iris contracts or dilates causing the pupil to be larger or smaller depending on the intensity of the light, thus controlling how much light enters the eye. Next the light goes through the lens, which focuses it by changing shape depending on whether light is being focused from near or far objects.

Finally, the focused light goes through a clear jelly in the center of the eye called the vitreous and falls on the retina, the lining in the back of the eye, where the light triggers photo receptors on the retina. There are several kinds of receptors, and they convert the light into electro-chemical signals that travel along nerve fibers to a nerve bundle called the optic nerve, which sends signals to the vision center in the back of the brain.

Some common eye conditions

Eye problems occur along this pathway of light from external object to the brain. The most common condition that almost everyone suffers as they pass 40 and begin to age, is when their ability to see close objects and small print diminishes. This has a technical name, presbyopia, and occurs when the lens loses its elasticity and is unable to focus on near objects. Most people deal with this by getting reading glasses. Another option is to have a LASIK procedure.

Many people have "floaters," tiny spots that move across the field of vision. They are noticed in bright light or outdoors on a bright day. These are normal, but they can indicate a serious problem. If you notice a sudden change in the type or number of spots or flashes, see your eye doctor as soon as possible.

Astigmatism is a condition in which there is blurred vision caused by either an irregularly shaped cornea or sometimes the curvature of the lens inside the eye. These irregularities prevent light from properly focusing in your eye.

Myopia, also known as nearsightedness, occurs when light from distant objects focuses in front of the retina instead of directly on it. Thus you cannot clearly see things in the distance.

Hyperopia, also known as farsightedness, is a condition in which things at a distance can be seen clearly but things close up may be blurry. It occurs when light from a distant object strikes the retina before coming into focus or, in other words, focuses behind the retina.

Some people have dry eyes, which occurs when the tear glands are underproductive. On the other hand, some have too many tears, caused by over sensitivity to light, wind, or temperature. These conditions can be handled easily by your eye doctor.

How do you know whether or not your eyesight is good? A common measurement is the 20/20 test, but this checks only visual acuity - whether you can see a figure at 20 feet that most people should be able to see at that distance. This cannot measure other aspects of good vision. How well can you see objects against their background? Can you track moving objects? Can you see colors? Do you have good depth perception? How quickly can your eyes focus? Vision is more complicated and dynamic than simple acuity.

Some more serious eye problems and diseases

Cataracts are a common condition caused when cloudy areas develop on the lens, causing cloudy or fuzzy vision and sensitivity to glare. They develop slowly and there is no pain, just a gradual lessening of clear vision as more of the lens becomes cloudy. When the entire lens is white, the cataracts are "mature" or "ripe" and cause severe vision problems. They can be treated by surgery.

Glaucoma is damage to your optic nerve from increased pressure in the eye called intraocular pressure. If damage to the optic nerve, which transmits images to the brain, continues, glaucoma will cause permanent loss of vision. Without treatment, glaucoma can cause total blindness within a few years. The pressure in your eye increases because the eye fluid isn't circulating normally in the front part of the eye. Normally, this fluid, called aqueous humor, flows out of the eye through a mesh-like channel. If this channel becomes blocked, the fluid builds up, causing glaucoma. Why this blockage occurs is unknown, but doctors do know that the condition can be inherited.

There are other less common causes of glaucoma including a blunt or chemical injury to the eye, severe eye infection, blockage of blood vessels in the eye, inflammatory conditions of the eye, and occasionally eye surgery to correct another condition. Glaucoma usually occurs in both eyes, but it may involve each eye to a different extent. There is no cure for glaucoma, but immediate treatment at an early stage can delay the progression, so regular checkups are very important for diagnosing glaucoma.

Age-related macular degeneration, or AMD, is the leading cause of severe vision loss in people over age 60. It occurs when the small central portion of the retina, known as the macula, deteriorates. The retina is the light-sensing nerve tissue at the back of the eye. Because the disease develops as a person ages, it is often referred to as age-related macular degeneration. Although macular degeneration is almost never a totally blinding condition, it can be a source of significant visual disability.
 

Diabetic retinopathy occurs when chronically high blood sugar from diabetes causes damage to the tiny blood vessels in the retina and they leak blood, distorting vision. In its most advanced stage, proliferative retinopathy, new abnormal blood vessels proliferate on the surface of the retina, which can lead to scarring and cell loss in the retina. There are no early warning symptoms, so it is crucial to have a comprehensive eye exam at least once a year. If there is bleeding, you will see these specks of blood as spots, floating in your vision. See your eye doctor immediately. Sometime the spots will clear. But bleeding can occur again. Untreated, proliferative retinopathy can cause severe vision loss, even blindness.

A detached retina occurs when the retina at the back of the eye becomes separated from its underlying supportive tissue. If it is not reattached quickly, vision may be permanently lost. The symptoms are floaters and flashes of light. Vision may become blurry. You may see a shadow or a curtain descend from the top of the eyes or across from the side.

Retinal detachment can be caused by injury. A tear in the retina can allow fluid to get behind it and cause the separation. Sometimes extreme nearsightedness can cause the retina to detach. Very nearsighted people have elongated eyeballs with thinner retinas, which are more likely to detach. On very rare occasions, the retina may become detached during surgery. Also, when new blood vessels grow as a result of diabetic retinopathy, they may push the retina away from its supportive tissue.

The retina can be reattached with laser surgery or sometimes with a freeze treatment called cryopexy, both of which "weld" the retina back into place. Ninety percent of detached retinas can be reattached successfully.

Keeping your eyes healthy: common sense, nutrition, and eye exercise

Regular checkups are the best defense against eye problems and diseases. In a comprehensive eye examination, your doctor may use eye drops to see inside your eye more clearly and examine your retina and optic nerve. If you have a particular concern about your eyes, take a friend or relative along on your visit to the eye specialist to listen and to help you with questions. Be sure to take notes. Click here for a comprehensive list of more than 20 questions you might want to ask. Be persistent with your questions. If the eye exam shows something serious, don't hesitate to get a second opinion.

Here are four common-sense things you can do to keep your eyes healthy. 

Nutrition

Eat foods that provide nutrients that are good for the eyes:

Eye exercises

There is some controversy about what eye exercises can accomplish. Be wary of claims that a certain course of exercise will improve your eyesight. Many vision experts contend there is little scientific evidence to support this. You will find a good discussion of this on the All About Vision website.

The eye is a remarkable -- you might almost say miraculous -- organ. Our eyes work so well and with so little attention that we practically take them for granted. For those who do suffer from eye injuries, it is nice to know that eyes have an extraordinary capacity to heal. And with just a little attention and foresight (no pun intended), we can keep them in good working order and enjoy the pleasure of good eyesight throughout a long life.