Presbyopia is the gradual loss of eyes' ability to focus on nearby objects. It is caused by an age-related process. Presbyopia generally is believed to grow from a gradual thickening and loss of flexibility of the natural lens inside human eye. These age-related changes occur within the proteins in the lens, making the lens harder and thus it loses its elasticity over time.
The most common correction for Presbyopia is the use of eyeglasses with bifocal lens.