What is the crystalline structure that refracts light rays onto the retina in the eye?

The lens is the transparent structure in the eye that plays a crucial role in focusing light onto the retina. It is flexible and can change shape to adjust for distance, allowing for clear vision whether an object is near or far. The ability to refract light rays means that the lens bends the incoming light to ensure it converges precisely on the retina, which is the light-sensitive layer at the back of the eye where visual information is processed. This function is essential for clear vision, making the lens fundamental in the process of sight.

In contrast to the lens, the cornea also refracts light, but it primarily provides initial focusing. The pupil regulates the amount of light entering the eye but does not play a role in refracting light rays. The retina is where images are received, but it does not have a refractive function, as it is not responsible for bending light. Thus, the lens is the correct answer as it directly engages in the action of refracting light to achieve focused vision.