What is the function of the iris in the human eye?

The iris plays a crucial role in regulating the amount of light that enters the eye, which is essential for clear vision in varying lighting conditions. It achieves this by adjusting the size of the pupil, the opening at the center of the iris. When the light is bright, the iris constricts to reduce the pupil size, limiting the light entering the eye and preventing damage to the retina. Conversely, in low-light conditions, the iris dilates the pupil to allow more light in, enhancing visibility. This automatic adjustment helps maintain optimal visual function and protects the sensitive structures within the eye. Understanding the iris's role helps appreciate how the human eye adapts to different environments to ensure effective sight.