The Greeks used this term to refer to "aged eyes", describing a physiological condition related to the gradual hardening of fibers in the crystalline lens. For most people, this change occurs sometime between the ages of 40 and 50, when reading material has to be held further from the eyes in order to be seen clearly.
At the onset of presbyopia, near vision begins to become blurry and the eyes have greater difficulty in shifting focus between distant and near objects. The ocular lens and areas surrounding the lens are quite simply not as flexible as they were previously. Some presbyopes only require correction with extra plus power for reading, while others need a multifocal prescription in order to be able to see both distant and near objects clearly.