Which structure changes shape to help focus images by adjusting its thickness?

Which structure changes shape to help focus images by adjusting its thickness?

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

Answer: (D)

Focus at different distances is achieved by accommodation, where the lens changes its curvature. The lens is flexible, and when the ciliary muscle contracts, it reduces tension on the zonular fibers, allowing the lens to become more curved and thicker. This increases its refractive power so light from nearby objects is focused on the retina. When viewing distant objects, the ciliary muscle relaxes, the zonules tighten, and the lens becomes flatter, reducing its focusing power. The pupil and iris control how much light enters but don’t adjust focus by changing thickness, and the sclera is the outer protective coat that doesn’t participate in accommodation.

Focus at different distances is achieved by accommodation, where the lens changes its curvature. The lens is flexible, and when the ciliary muscle contracts, it reduces tension on the zonular fibers, allowing the lens to become more curved and thicker. This increases its refractive power so light from nearby objects is focused on the retina. When viewing distant objects, the ciliary muscle relaxes, the zonules tighten, and the lens becomes flatter, reducing its focusing power. The pupil and iris control how much light enters but don’t adjust focus by changing thickness, and the sclera is the outer protective coat that doesn’t participate in accommodation.