What is the site where nerve fibers from each eye crossover to the opposite side?

The correct answer is chiasm, specifically referring to the optic chiasm. This structure is vital in the visual pathway as it is where the nerve fibers from the retina of each eye cross to the opposite side of the brain. This crossover allows visual information from the right visual field of each eye to be processed in the left hemisphere of the brain and vice versa for the left visual field. This anatomical arrangement is crucial for depth perception and a unified field of vision.

The optic nerve refers to the bundle of nerve fibers that carry visual information from each eye to the brain, but it does not involve crossing over. The retina is the part of the eye that converts light into neural signals but is not involved in the crossover process. The cerebral cortex is involved in higher-order processing of visual information but does not involve the direct crossover of the nerve fibers; it's where the information is ultimately interpreted after being relayed from the optic chiasm. Thus, the chiasm is the specific location where this critical crossover occurs, facilitating the integration of visual input from both eyes.