Which structure of the eye is primarily responsible for focus?

The lens of the eye plays a crucial role in focusing light onto the retina, which is necessary for clear vision. It works in conjunction with the cornea but is primarily responsible for the adjustment of focus. The lens can change its shape through a process known as accommodation, allowing it to focus light from objects at various distances. When viewing a distant object, the lens flattens, while it thickens to focus on closer objects. This dynamic adjustment is essential for clear vision across a range of distances, making the lens the key structure for focus in the eye.

In contrast, the retina is responsible for receiving the focused light and converting it into neural signals that are sent to the brain. The iris controls the size of the pupil and thus regulates the amount of light entering the eye, but it does not adjust focus. The cornea contributes significantly to bending light as it enters the eye but does not have the fine-tuning ability that the lens possesses.