What is the function of the iris in the eye?

The iris plays a crucial role in regulating the amount of light that enters the eye by controlling the size of the pupil. It is the colored part of the eye, and its muscles adjust the size of the pupil in response to varying lighting conditions. In bright light, the iris constricts the pupil, reducing the amount of light that can enter; conversely, in dim light, it dilates the pupil to allow more light in. This regulation helps protect the retina and aids in the overall clarity of vision, making its function vital for proper visual perception in different environments.

The other options do not accurately describe the function of the iris. Focusing light onto the retina primarily involves the lens, while color and shape detection is the responsibility of the photoreceptors in the retina. Additionally, the optic nerve connects the eye to the brain but does not involve the iris's function.