Final answer:
The transparent structure in the eye that helps focus images is called the lens, which fine-tunes light passing through the pupil after the cornea has refracted it, ensuring a clear image on the retina.
Step-by-step explanation:
The flexible, transparent structure in the eye that helps focus an image on the back of the eye's interior is called the lens. The cornea and lens work together to refract light and focus it onto the retina. Light first passes through the cornea, which is the clear front surface of the eye, then it continues through the pupil and enters the lens. The lens is responsible for fine-tuning the focus of the light so that a clear image is projected onto the retina, where photoreceptors convert the light signals into nerve impulses that travel to the brain.