The part of the eye responsible for focusing light onto the retina is the lens. The lens is a transparent structure that adjusts its shape to change the focal distance, allowing us to see objects clearly at different distances. When light enters the eye, it is refracted by the lens and directed onto the retina, where photoreceptor cells convert the light into electrical signals for the brain to interpret as images. Proper lens function is essential for vision, and any abnormalities can lead to refractive errors.