Presbyopia

In our youth, the lens is very flexible and accommodates easily for close focus. As we mature, the lens grows in a fashion similar to that of a tree trunk. Layers of protein are deposited on the outside surface (like the rings on a tree trunk), causing the lens to become thicker, denser, and less flexible. When that occurs, close focusing becomes difficult, and people start using magnifying glasses to focus up close without eyestrain. This usually begins in the mid-forties and gets progressively worse for about 15 years.