In a previous example, you saw that when reading a book, your lens is rounder or more convex, but when you look up to see a student entering the library, your lens becomes flatter or less convex. What muscle action results in the lens becoming less convex?

• A. Ciliary muscles contract.
• B. Ciliary muscles relax.
• C. Pupillary constrictors contract.
• D. Pupillary dilators relax.

Answer: (B)

Verified step by step guidance

1. Understand the anatomy of the eye, specifically the role of the lens and ciliary muscles. The lens changes shape to focus light on the retina, and this process is known as accommodation.
2. Recognize that the ciliary muscles are responsible for changing the shape of the lens. When these muscles contract, they allow the lens to become more convex, which is necessary for focusing on nearby objects.
3. Identify the action required for the lens to become less convex. For distant vision, the lens needs to flatten, which occurs when the ciliary muscles relax.
4. Consider the physiological mechanism: when the ciliary muscles relax, the tension on the lens increases, causing it to flatten and become less convex, suitable for viewing distant objects.
5. Differentiate between the roles of ciliary muscles and pupillary muscles. Pupillary constrictors and dilators control the size of the pupil, not the shape of the lens. Therefore, the relaxation of ciliary muscles is the correct action for the lens to become less convex.