The inner lining of the back portion of the eye is the retina. The lens is a convex disk that is held in place by muscles. The outer lining of the lens is called the capsule. The lens changes shape by contracting and relaxing the ciliary muscles to change the focal distance of the eye by making the lens thicker or thinner. The younger lens can change shapes rather dramatically allowing reading at very close distances when the lens is thicker.
Cataracts occur in the lens of the eye.
Aging and Presbyopia Aging causes several effects in the eye. One is a stiffening of the lens and a progressive loss of the lens' ability to change shapes. The individual finds that reading must be done at greater distances initially and then with the aid of reading glasses. This stiffening of the lens with age is termed presbyopia . Presbyopia is a universal phenomenon.