Presbyopia occurs as part of normal aging and is not considered to be an eye disease. The process occurs gradually over a number of years.
Symptoms are usually noticeable by age 40–45 and continue to develop until the process stabilises some 10–20 years later. The result is that it is more difficult to read at close range.
It is when the natural lens hardens and loses elasticity, it loses ability to focus on objects at any distance. It can be corrected with Refractive Surgery.