How does the eye primarily adjust to focus on near objects?

The primary mechanism by which the eye adjusts to focus on near objects is by changing the shape of the lens. This process is known as accommodation. When focusing on objects that are close, the ciliary muscles surrounding the lens contract, allowing the lens to become thicker and more curved. A thicker lens increases its refractive power, enabling light rays from nearby objects to be focused sharply on the retina.

In contrast, when focusing on distant objects, the ciliary muscles relax, causing the lens to flatten, which is necessary for the proper focusing of light from farther away. The cornea, while it plays a significant role in focusing light due to its curvature, does not change shape to accommodate for near vision. Pupil dilation, while it can aid in depth of focus and aspect of visual clarity, does not directly change the way the eye accommodates for near objects. The extraocular muscles are involved in moving the eye but do not influence the eye’s ability to adjust focus. Therefore, the adjustment of the lens is the key factor in achieving clear vision for near objects.