Which part of the eye is responsible for focusing light onto the retina?

The lens is crucial in the eye's ability to focus light onto the retina. It is a transparent, flexible structure located behind the iris and the pupil. The primary function of the lens is to change shape—a process known as accommodation—to adjust the focus for objects at varying distances. When looking at something far away, the lens flattens, and when focusing on something close, it becomes more rounded. This ability allows the lens to bend light rays appropriately so that they converge sharply on the retina, creating a clear image.

While the ciliary body plays a role in adjusting the lens's shape through the control of muscles, it does not directly focus the light itself. The iris functions to regulate the amount of light entering the eye by adjusting the size of the pupil, and the cornea is responsible for the majority of the eye's total focusing power due to its curvature and refractive properties. However, it is the lens that fine-tunes this focus, particularly for objects at different distances. Thus, the lens is the correct part of the eye that is primarily responsible for focusing light onto the retina.