Which structure is responsible for adjusting the focus of light on the retina?

The lens is the structure responsible for adjusting the focus of light on the retina. It is a flexible, transparent structure located behind the iris and pupil, which plays a crucial role in the eye's ability to focus on objects at varying distances.

When looking at something far away, the lens flattens to allow light rays from distant objects to converge precisely on the retina. Conversely, when focusing on nearby objects, the lens becomes thicker and more curved. This adjustment process is known as accommodation and is essential for clear vision across different distances.

The cornea, while also involved in focusing light, does not adjust its shape significantly. Instead, it provides most of the eye's optical power due to its curved surface. The pupil regulates the amount of light entering the eye but does not play a role in adjusting focus. The iris controls the size of the pupil and therefore influences light entry but has no direct involvement in the focusing process. Thus, the lens is uniquely suited for this critical task of focusing light on the retina, adapting its shape to ensure that vision remains clear and sharp across a range of distances.