How your eyes work
Our eye is like a camera, focusing the light that enters the eye to form a clear image on the retina. Most visual problems are caused by the way the cornea of the eye refracts (or bends) the light. If the cornea is misshapen in any way, that clear image cannot be formed correctly.

Myopia (nearsightedness)
Myopia is when people see near objects more clearly, but distant objects are blurry. Due to the steepness of the cornea, this occurs when light rays entering the eye are focused in front of the retina instead of directly on it.

Hyperopia (farsightedness)
Hyperopia is when people see far away objects more clearly, but close objects are blurry. Due to a flatter cornea, this occurs when light rays entering the eye are focused behind the retina instead of directly on it.

Astigmatism
Astigmatism is the result of having a corneal surface that is not regular in shape. People with astigmatism actually have a cornea that is shaped more like a football than a basketball. The result of having a cylinder shape to the cornea is two focal points instead of one.

Cataracts
A cataract is the clouding of the lens in the eye. Normally, light passes through the clear lens and is focused onto the retina. However, as a result of the natural aging process, the lens gradually becomes cloudy and this blocks the passage of light through the eye causing distorted or blurred vision.

Glaucoma
Glaucoma is a condition in which the pressure of fluid in the eyeball is abnormally high -- higher than the eye can tolerate over a long period of time. Most ophthalmologists agree that when pressure in the eye -- referred to as intraocular pressure -- is higher than normal, the risk of pressure-related damage significantly increases.