Emmetropia

When an eye's optical power is perfectly matched to its length, the eye is said to be emmertropic. Emmetropia is the medical tern for 20/20 vision needing no corrective lenses, contact lenses, or reading glasses. It occurs because the optical power of the eye can perfectly focus an image to the retina, giving them "perfect" vision.

The opposite of emmertropia is ametropia. With ametropia, the focal point of the eye is some distance in fron tof or behind the retina.

Hyperopia

Hyperopia is more commonly known as farsightedness. As the name suggets, people with farsightedness are able to focus on objects that are further away, but have difficulty focusing on objects which are very close. This is because they eyeball is shorter than normal, which prevents the crystalline lens in the eye from focusing correctly on the retina. About  a fourth of the population are afflicted with hyperopia. Hyperopia can lead to chronic glaucoma, a more serious condition, later in life.

A family history of hyperopia is a risk factor for devloping hyperopia. Often babies are born with hyperopia but they can ususally outgrow the condition as the eye develops into the correct shape.

Myopia

Myopia is the medical term for what most people call nearsightedness. It is a condition where you can see objects clearly only when they are closer, but when objects are further away you can't focus on them. Myopia usually develops in early childhood, though it sometimes develops in early adulthood. In rare cases, myopia can lead to more serious conditions such as retinal detachment.

Myopia is considered a genetic disorder. If you parents are nearsighted, you are at greter risk of also being nearsighed. Another risk factor is "near work"-work involving fine detail or focusing on close objects.

Presbyopia

As people gt older, usually when they hit their mid to late 40s, a condition called presbyopia can set in. Presbyopia is the inability to focus on objects near the eye. One usally notices that it is harder to read our use the computer. Bifocals or reading glasses are a way to remedy it.

Presbyopia is a natural consequence of the aging process. There is no cure, though researchers are constantly looking for one. Even if a someone ha never had vision problems before, they can still develop presbyopia. It maybe seem to occur suddenly, but actually occurs over a long period of time. Symptoms include having to hold things at arm's length to see them clearly, eye strain, fatigue, and headaches from near work.

Amblyopia

Amblopia, commonly called lazy eye, occurs when one eye develops differently than the other eye, cauisng one eye to be weaker than the other. Sometimes a difference in focusing ability caues one eye to be used more often. Other times, they eyes are misaligned, causing one eye to "shut off" to avoid double vision. Regardless of the cause, the result is a weakened, or amblyopic eye.

It's hard to spot amblyopia. Sometimes a child will noticeably favor one eye over the other. Another possible symptom is the child frequently bumping into things on one side. The best way to tell if your child has lazy eye is through a complete eye exam around six months and three years. Early diagnosis can prevent amblypia from leading to more serious problems such as loss of the ability to see three dimensions or functional blindness in the amblyopic eye.

Astigmatism

Sometimes the cornea is irregularly shaped, causing the eye to focus an object on two difference areas of the retina. This is known as astigmatism. For the cornea to bend light correctly, it should be dome-shaped, like a basketball. Astigmatic corneas are shaped more like a football. This causes a distorted view when looking at objects when are close-up and far away.

The cause of astigmatism is unknown. Astigmatism is often associated with myopia or hyperopia, and usually occurs from birth. It may be hereditary, or it maybe be caused by factors such as pressure on the cornea, incorrect posture, or increased use of the eye for "near work."

Computer Vision Syndrome

Computer vision syndrome (CVS) affects three out of the four computer users. It is a series of symptoms related to extended periods of computer usage. Though it is no cause for panic, measures can be taken to relieve symptoms of CVS.

CVS can appear as a variety of symptoms. Headaches, eye strain, neck and back aches, sensitivity to light, blurred vision, double vision, and dry or irritated eyes are all possilbe problems related to CVS.