Which structure allows a certain amount of light into the retina based on stimulation?

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

Answer: (B)

Light entering the eye is regulated by the pupil, the opening formed by the iris. Its size changes in response to stimulation from light via the autonomic nervous system: bright light makes the pupil constrict to limit light reaching the retina, while dim light makes it dilate to allow more light in. This adjustment helps the retina receive an appropriate amount of light for clear vision. The iris is the colored part that contains the muscles controlling the opening; the cornea is the transparent front surface that helps focus light but doesn’t regulate how much enters; the retina is the light-detecting layer inside the eye and does not control entry.