Which part of the eye is primarily responsible for focusing light?

The lens is primarily responsible for focusing light that enters the eye. It works together with the cornea to refract light, but its key function is to change shape—becoming thicker or thinner—through a process called accommodation. This dynamic adjustment allows the lens to focus light precisely onto the retina, which is essential for clear vision at varying distances.

While the cornea contributes to the initial refraction of light, it has a fixed shape and cannot change its curvature to the same extent as the lens. The iris, on the other hand, is involved in controlling the size of the pupil and the amount of light entering the eye, but it does not play a direct role in focusing light. The retina is responsible for receiving light and converting it into neural signals for the brain to interpret, but it is not involved in the focusing process itself. Therefore, the lens is the key structure for fine-tuning focus, making it the correct answer.