Accommodation for Distant Vision Steps:

• Distant objects produce nearly parallel light rays needing minimal lens refraction.
• Ciliary muscle relaxes to release pull on the lens equator.
• Suspensory ligaments (zonules) tighten under elastic recoil.
• Lens flattens and thins to reduce convexity for clear focus.

Why C is correct:

• Relaxation of the ciliary muscle increases zonular tension, stretching the lens thinner for distant focus, as defined in the Helmholtz-Trouton theory of accommodation.

Why the others are wrong:

• A: Contraction thickens the lens for near vision, not distant.
• B: Contraction slackens zonules, causing lens thickening, not thinning.
• D: Relaxation thins the lens, not thickens it.

Final answer: C