As you can probably guess, the other set of muscles of the iris cause the pupil to shrink, or constrict. This happens when you go from darkness to light, like when you put on the light in the middle of the night to see what you’re doing in the bathroom.

Immediately behind the iris is the lens, which changes shape in order to focus images of things at different distances from you on your retina. This ability of the lens to change shape to focus images on the retina as distance changes is called accommodation. Unfortunately, as you age, your lens will lose some of the ability to accommodate, which will result in an inability to focus on nearby objects. This change is called presbyopia, which literally means “old eye.” Presbyopia is also called farsightedness, and you may have noticed that older people sometimes hold a book or a newspaper at arm’s length when they’re trying to read it, particularly if they’re not wearing their glasses. This is just one of many physical changes you have to “look forward to.”