What do you call the structure in the eye that causes the largest amount of refraction?

Tear film/cornea: The very front part of the eye is responsible for the greatest amount of refraction (or focusing) of light rays entering the eye. Approximately 2/3 of refraction of light rays occurs at the front surface of the cornea, actually at the air-tear film/cornea interface. The tear film coats the surface of the cornea. The other 1/3 of refraction occurs in the crystalline lens inside the eye.

Cornea: The cornea (with its outer tear film) does about 2/3 of the refraction of light entering the eye. The lens does about 1/3.

The cornea: The clear window where a contact lens would rest on the eye.

Cornea: The cornea has the highest refracting power in the eye, followed by the natural lens.