What is the primary function of the retina?

The primary function of the retina is to perceive light. The retina is a thin layer of tissue located at the back of the eye that contains photoreceptors known as rods and cones. These photoreceptors are sensitive to light and play a crucial role in converting light into electrical signals. Once the light signals are generated, they are transmitted to the brain through the optic nerve, where they are processed to form visual images.

The other functions mentioned do not pertain directly to what the retina does. For instance, controlling eye movement involves muscles and nerves outside of the retina's role. Protecting the eye is mainly the function of external structures like the eyelids, eyelashes, and tear film, which shield the eye from foreign objects and debris. Focusing images is primarily the job of the lens, which adjusts its shape to ensure that light is precisely focused onto the retina for clear vision. Thus, the correct answer emphasizes the critical role of the retina in capturing and processing light, making it essential for vision.