Which visual adjustment mechanism of the eye helps in focusing on objects at varying distances?

The mechanism responsible for focusing on objects at varying distances is accommodation. This process involves the eye's lens changing shape to adjust its focal length, allowing us to see objects clearly whether they are near or far. When viewing a distant object, the ciliary muscles relax, causing the lens to become flatter. Conversely, when focusing on a nearby object, the ciliary muscles contract, making the lens thicker and more rounded. This dynamic adjustment ensures that light rays entering the eye focus correctly on the retina, providing a clear image.

The other options refer to different visual processes. For example, concentration relates to attention rather than focusing mechanics, convergence refers to the inward movement of both eyes toward each other when looking at close objects, and adaptation involves changes in the eyes' sensitivity to light in varying conditions. While all are important for visual perception, accommodation specifically plays the critical role in adjusting focus for different distances.