It begins somewhere between the age of 40 and 50: The lens and the ring muscle inside your eyes might lose elasticity. The eye is no longer able to automatically adjust and zoom in on different distances, a process enabled by what experts call accommodation. It makes the lens of the eye bend to adjust to the distances.
However, if this process does not work as nature intended, this causes problems with close-up vision. If the lens maintains a flat shape when looking at objects that are close-by, its refractory force is significantly impaired. Consequently, light beams that penetrate the eye from near-by are bundled behind the retina and deliver a blurred image.
Farsighted people may encounter this problem much sooner. Hyperopic people have excellent long range vision, but do have problems seeing things that are close-up. The reason: The eyeball is too short and the incoming rays of light are not accurately depicted on the retina.
Bifocal and trifocal lenses are the predecessors of progressive lenses. They are the ideal solution for those who do not like progressive lenses or have trouble using them. Some people still prefer them, however, these types of lenses provide just an alternative and require compromises, since the join in lens creates an image leap and these types of glasses cannot cover all vision ranges.