Human eye cross-sectional view. Courtesy NIH National Eye Institute

Age-related macular degeneration (AMD) is a disease which blurrs the central, sharp vision of the eye by damaging the macula, the part of the eye which allows you to see fine details. It is the main cause of vision loss in Americans who are 60 or more years old. It can progress so slowly that it isn't noticed or it can progress quickly.

The macula is at the center of the back of the eye, part of the tissue which lets you see. Light striking it is converted to electrical nerve signals which are sent to the brain.

There are two types of macular generation.

Normal vision. Courtesy NIH National Eye Institute
The same view with age-related macular deneneration.

Wet AMD

Wet AMD is caused by abnormal blood vessels behind the retina growing under the macula. The new blood vessels tend to be fragile, break easiy and leak blood, which raises the macula from it's normal place. This rapidly damages the macula. With wet AMD loss of central (sharp) vision can be rapid and it is always considered to be advanced AMD and more severe than the dry form. An earyl symptom of wet AMD is straight lines appearing wavy. Anyone who sees this or other changes in vision should contact their eye doctor at once to get a comprehensive dilated eye examination.

Dry AMD

More information on the subject is available here.