Presbyopia occurs when the eye's lens loses its ability to focus on objects that are near. Often confused with farsightedness, presbyopia is an age-related condition caused by a loss of flexibility in the lens and a weakening of the surrounding muscles. It usually begins to affect people in their early 40s, requiring the use of glasses or bifocals for reading. Unlike farsighted patients, people with presbyopia will not loose their distance vision (unless they develop an eye disease)