What structure in the eye helps to focus light onto the retina?

The lens is a critical structure in the eye responsible for focusing light onto the retina. It is a transparent, flexible structure that can change its shape through the action of ciliary muscles. This capability allows the lens to adjust its focal distance, enabling the eye to focus on objects at various distances. When viewing something close, the lens becomes more rounded, increasing its refractive power. Conversely, when looking at distant objects, the lens flattens. This focusing ability is essential for clear vision, as it ensures that light rays converge properly on the retina, where photoreceptor cells convert the light into neural signals.

While the cornea also plays a significant role in refracting light, it provides most of the eye's total optical power but does not have the same degree of adjustable focusing capability as the lens. The pupil controls the amount of light entering the eye, and the vitreous body, a gel-like substance that fills the eye, helps maintain its shape but does not contribute directly to focusing light.