Final answer:
The iris controls light entry into the eye by adjusting pupil size, acts as a muscle, and defines eye color. It ensures optimal vision by regulating light and contributing to individual visual identity.
Step-by-step explanation:
Three characteristics of the iris of the eye are that it:
- Adjusts the amount of light coming into the eye.
- Is a muscle that controls the size of the pupil.
- Is the colored part of the eye that contributes to eye color.
The iris plays a crucial role in vision by regulating light intake, constricting or dilating the pupil in response to varying light conditions. Functioning akin to the aperture of a camera, it works to permit the optimal amount of light to enter the eye so that the lens can focus it correctly onto the retina. The selective contraction and relaxation of the smooth muscle tissue in the iris make this regulation possible, while the unique coloration of the iris contributes to the aesthetics and individuality of each human eye.