Final answer:
The eye adjusts its focusing power for distant and close objects through relaxation and accommodation. For distant vision, the eye is relaxed with parallel light rays easily converging on the retina.
For close vision, the lens becomes thicker and more powerful to focus diverging light rays from close objects onto the retina.
Step-by-step explanation:
The process of adjusting vision to focus on distant and close objects involves various changes within the eye's structure. For distant objects, light rays entering the eye are nearly parallel and therefore require less refraction to focus on the retina. This state is called relaxed vision, and it is when the eye is at its least powerful state in terms of bending light.
However, when focusing on close objects, the light rays are diverging more and the lens within the eye needs to become more powerful to converge these rays onto the retina. This adjustment is known as accommodation and is achieved by the lens becoming thicker, an action controlled by the contraction of the ciliary muscles surrounding the lens.
When viewing close objects, the lens is at its greatest power for the most precise focus on the retina, which is known as being fully accommodated. The change in the lens and eye focus is similar to how you would adjust a camera lens to get a clear image of near or far objects.
In the case of nearsightedness, an individual may see near objects clearly due to the eyes' ability to focus these images on the retina, whereas distant objects appear blurred because their images focus in front of the retina.
Instruments like microscopes and telescopes are designed to mimic distant vision by producing images that allow the eye to remain in a relaxed state.