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

The lens is the part of the eye that is responsible for focusing light onto the retina. It works by changing its shape—becoming thicker or thinner as needed to adjust the focus for objects at varying distances. This process is known as accommodation and is vital for producing clear images. When light rays enter the eye, they pass through the cornea and the pupil before reaching the lens. The lens precisely fine-tunes the focus, ensuring that the light is directed accurately onto the retina, where the image is processed and sent to the brain.

In this context, the other structures play different roles. The cornea provides the majority of the eye's optical power and helps to refract light, while the iris regulates the amount of light entering the eye by controlling the size of the pupil. The pupil itself is merely an opening through which light passes but does not focus light.