What happens to the lens when focusing on near objects?

What happens to the lens when focusing on near objects?

• A. The lens becomes flatter.
• B. The ciliary muscles relax, lengthening the lens.
• C. Ciliary muscles contract, making the lens more rounded.
• D. The pupil constricts to increase depth of field.

Answer: (C)

Focusing on near objects relies on accommodation, where the lens increases its optical power by becoming more curved. When the ciliary muscles contract, they reduce tension on the zonular fibers that hold the lens, allowing the lens to thicken and round up. This increased curvature raises the lens’s refractive power, shortening the focal length so light from near objects is focused on the retina. In contrast, relaxing the ciliary muscles flattens the lens for distant vision. Pupil constriction can help with depth of field, but it doesn’t change the lens shape.

Focusing on near objects relies on accommodation, where the lens increases its optical power by becoming more curved. When the ciliary muscles contract, they reduce tension on the zonular fibers that hold the lens, allowing the lens to thicken and round up. This increased curvature raises the lens’s refractive power, shortening the focal length so light from near objects is focused on the retina. In contrast, relaxing the ciliary muscles flattens the lens for distant vision. Pupil constriction can help with depth of field, but it doesn’t change the lens shape.