Which structure is primarily responsible for the refraction of light entering the eye?

The cornea is primarily responsible for the refraction of light entering the eye due to its unique shape and transparency. When light rays enter the eye, they first encounter the cornea, which has a convex shape that causes the light to bend or refract. This initial refraction is crucial because it directs light towards the pupil and lens to ensure that it is properly focused on the retina.

The cornea has a significantly higher refractive index compared to air and contributes to approximately two-thirds of the eye's total optical power. Its curvature is specifically designed to help focus the incoming light, allowing for clearer vision at various distances.

Other structures, such as the iris, ciliary body, and pupil, have important functions in the eye, but they are not primarily responsible for light refraction. The iris contributes to controlling the amount of light that enters the eye by adjusting the size of the pupil, while the ciliary body is involved in adjusting the shape of the lens for accommodation and regulating the production of aqueous humor. The pupil serves as the opening through which light passes but does not play a direct role in the bending of light itself.