To focus on objects closer than 20 feet,

Question

BlackTom AI · Accepted Answer

When considering how the eye focuses on objects closer than about 20 feet, several anatomical changes are at play.
Option 1: 'the lens must become flatter.' This is incorrect for near focusing; to see near objects clearly, the lens actually becomes thicker and more curved, not flatter, increasing its optical power.
Option 2: 'the cornea must move inward.' The cornea does not move inward as part of accommodation; its shape remains relatively static during near focus, so this statement misrepresents the mechanism.
Option 3: 'the ciliary muscles must contract.' This is the central action of accommodation for near objects: contraction of the ciliary muscle reduces tension on the suspensory ligaments, allowing the lens to round up and increase its refractive power to focus on close items.
Option 4: 'the suspensory ligaments increase tension on the lens.' In fact, when the ciliary muscle contracts, the suspensory ligaments relax, which enables the lens to become thicker; increasing tension would flatten the lens, opposing near focus.
Option 5: 'the retina must bend.' The retina does not bend as a mechanism for focusing; focusing is achieved by changing the lens shape, not by altering retinal curvature.
In summary, the correct mechanistic statement is that the ciliary muscles contract to enable accommodation for near objects, while the other options describe actions that would oppose or are unrelated to near-focus accommodation.

To focus on objects closer than 20 feet,单项选择题

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