The image you see of the world is focused onto the seeing layer at the back of the eye called the retina. The central area of the retina is called the macula; it sees fine detail and colour. Standing in front of a mirror, the macula sees an area the size the face.
The macula is exposed to more natural light over a lifetime than the rest of the retina and so, it is quite usual for the macula to change with increasing age. This causes some of the cells of the macula to degenerate (break down) and function less well. Age related macular degeneration (ARMD) resembles the tarnishing of silver on an older mirror – the image seen is dull and blurred or may be disturbed and distorted where the silver has flaked away.
Age changes of the retina are identified by an eye specialist looking into the eye but with mild age changes being quite usual when people are older, some doctors may reserve using the term macular degeneration for when they are more pronounced or affecting the vision, so as to avoid unnecessary worry or alarm. Increased life expectancy means that more people will develop these changes during their lifetime.