Which structure within the eye helps to focus light on the retina?

The lens is the structure in the eye that plays a crucial role in focusing light onto the retina. It is a transparent, flexible structure located behind the iris and pupil that adjusts its shape to change the focal distance of the eye. This ability to change shape ensures that light rays entering the eye are properly refracted to create a clear image on the retina, which is essential for sharp vision.

While the cornea also contributes to the eye's focusing ability, it primarily handles the majority of light refraction as it enters the eye. The iris controls the amount of light that enters the eye by adjusting the size of the pupil but does not participate directly in the focusing process. The sclera, which is the outer protective layer of the eye, does not play a role in focusing light either. Thus, the lens specifically fulfills the function of focusing light onto the retina, making it the correct answer.