During accommodation for near vision, which sequence occurs?

During accommodation for near vision, which sequence occurs?

• A. Ciliary muscle relaxes, zonular fibers tighten, lens flatten.
• B. Ciliary muscle contracts, zonular fibers relax, lens becomes thicker and more curved.
• C. Pupil constricts, iris changes, lens thickens.
• D. Retina changes, optic nerve.

Answer: (B)

When focusing on near objects, the eye increases its optical power by changing the lens shape. The ciliary muscle contracts, which releases tension on the zonular fibers (the suspensory ligaments). With that tension reduced, the lens, aided by its natural elasticity, becomes more circular and thicker, increasing its curvature and refractive power so light from a close object is focused on the retina. This contraction is driven by the parasympathetic pathway to the ciliary muscle. While pupil constriction can accompany the near reflex, the essential sequence for changing focus is the ciliary muscle contracting, zonular fibers relaxing, and the lens thickening. The opposite sequence—ciliary muscle relaxing and the lens flattening—occurs for distant vision.

When focusing on near objects, the eye increases its optical power by changing the lens shape. The ciliary muscle contracts, which releases tension on the zonular fibers (the suspensory ligaments). With that tension reduced, the lens, aided by its natural elasticity, becomes more circular and thicker, increasing its curvature and refractive power so light from a close object is focused on the retina. This contraction is driven by the parasympathetic pathway to the ciliary muscle. While pupil constriction can accompany the near reflex, the essential sequence for changing focus is the ciliary muscle contracting, zonular fibers relaxing, and the lens thickening. The opposite sequence—ciliary muscle relaxing and the lens flattening—occurs for distant vision.