Presbyopia is a refractive error that makes it hard for middle-aged and older adults to see things up close. It happens because the lens (an inner part of the eye that helps the eye focus) stops focusing light correctly on the retina (a light-sensitive layer of tissue at the back of the eye).
Presbyopia is a normal part of aging. Everyone gets presbyopia as they get older, usually after age 45. Many people have another refractive error in addition to presbyopia.