Which structure regulates the amount of light reaching the retina by changing the size of the opening?

Which structure regulates the amount of light reaching the retina by changing the size of the opening?

• A. Pupil
• B. Cornea
• C. Iris
• D. Lens

Answer: (C)

The iris is the structure that regulates how much light reaches the retina by changing the size of the opening, which is the pupil. The iris acts like a diaphragm around the pupil and has two muscle groups: the sphincter pupillae, which constricts the pupil to let in less light, and the dilator pupillae, which dilates it to allow more light in. In bright conditions, the parasympathetic system triggers constriction, protecting the retina from excess light. In dim conditions, the sympathetic system triggers dilation to improve visibility. The cornea and lens adjust focus, but they don’t control the amount of light entering.

The iris is the structure that regulates how much light reaches the retina by changing the size of the opening, which is the pupil. The iris acts like a diaphragm around the pupil and has two muscle groups: the sphincter pupillae, which constricts the pupil to let in less light, and the dilator pupillae, which dilates it to allow more light in. In bright conditions, the parasympathetic system triggers constriction, protecting the retina from excess light. In dim conditions, the sympathetic system triggers dilation to improve visibility. The cornea and lens adjust focus, but they don’t control the amount of light entering.