What structure in the eye primarily contributes to focusing light onto the retina?

The ability to focus light onto the retina involves both the cornea and the lens. These structures work together but have distinct roles in the process of refraction, which is the bending of light as it passes through different mediums.

The cornea, being a transparent structure, is the first part of the eye that light encounters. It has a fixed curvature that provides significant refractive power, bending the incoming light rays toward the center of the eye. Because the cornea does not change shape, it plays a crucial role in providing a strong initial focus.

The lens, located behind the cornea, has the unique ability to change its shape thanks to the ciliary muscles. This accommodation allows the lens to fine-tune the focus of light on the retina, adjusting for distance and ensuring that objects at varying distances are viewed clearly.

Together, the cornea and lens ensure that light rays converge precisely on the retina, allowing for clear vision. Therefore, the combined function of both structures is essential for proper optical focus in the eye, making the option that includes both the cornea and lens the most accurate choice. The sclera, while important as the outer protective layer of the eye, does not play a role in focusing light.