What is the function of the iris?

• A. The hole that lets light into the eye
• B. To give the eye shape
• C. to regulate the size of the pupil
• D. The jellylike tissue behind the lens

Answer: (C)

The iris functions as an adjustable diaphragm for the eye, regulating the size of the pupil to control how much light enters. It is a colored ring around the pupil that contains two muscle layers: one that constricts the pupil in bright light and another that dilates it in dim light. When the environment is bright, the pupil becomes smaller to limit light and protect the retina; in dim light, it grows larger to let in more light for better vision. The hole that lets light in is the pupil, not the iris, and the jellylike tissue behind the lens is the vitreous humor, so those parts aren’t the iris’s job. The iris’s main role is adjusting pupil size to maintain appropriate light levels for clear vision.