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

The lens is the critical component of the eye that focuses light onto the retina. It achieves this through a process called accommodation, where the shape of the lens adjusts to focus light rays that are coming from objects at varying distances. When viewing objects that are far away, the lens flattens, while it becomes more rounded to focus on nearby objects. This ability to change shape ensures that a clear image is formed on the retina, where photoreceptor cells convert the light signals into neural messages that the brain processes as visual images.

The cornea also plays a significant role in refracting light as it enters the eye, but it primarily provides the initial bending of light and does not have the same dynamic focusing capability as the lens. The iris and pupil, on the other hand, regulate the amount of light that enters the eye and control the size of the pupil, but they do not directly focus light onto the retina. Thus, the lens is the main structure responsible for fine-tuning the focus of light.