Which structure does photoreception primarily occur in the eye?

Photoreception primarily occurs in the retina, which is the innermost layer of the eye that contains specialized cells called photoreceptors. These photoreceptors include rods and cones, which are responsible for detecting light and converting it into electrical signals that can be processed by the brain. Rods are sensitive to low light levels and are essential for night vision, while cones are responsible for color vision and function best in bright light.

The other structures mentioned do not play a direct role in photoreception. The iris is responsible for controlling the amount of light entering the eye by regulating the size of the pupil. The cornea, as the eye's outermost layer, helps to focus light but does not contain photoreceptors. The sclera is the white, protective outer covering of the eyeball and serves a structural role without being involved in the photoreceptive process. Therefore, the retina is the critical structure for photoreception in the eye.