visual pathway (retina to cortex)

The visual pathway is the chain of brain stations that carries what your eyes catch all the way to the part of the brain that lets you actually see it. Light first lands on the retina, a paper-thin sheet of light-sensitive cells lining the back of each eyeball. The retina turns that light into tiny electrical pulses, much like a camera sensor turning a scene into a digital signal. Those pulses then leave the eye and travel inward, hop through a relay station, and finally arrive at the back of the brain, where they are read out as the picture you experience.

Trace the route step by step. The pulses run out of the eye along a thick bundle of nerve fibers called the optic nerve. The two optic nerves, one from each eye, meet at a crossing point where some fibers swap sides, so signals from your left field of view end up on the right side of the brain and the right field on the left side. From there the fibers reach the thalamus, a deep relay hub that sits in the middle of the brain and forwards almost all incoming senses; the vision part of it tidies and routes the signals. Finally a fresh set of fibers fans out to the visual cortex, the wrinkled outer layer at the very back of the head, which pieces the signals together into edges, motion, color, and the full scene you recognize.

Because vision relies on this whole relay line, where it breaks matters as much as whether it breaks. Damage at the eye or optic nerve can dim or blind one eye, while damage further along, after the crossing point, knocks out the same half of the visual world in both eyes at once. Mapping exactly which slice of sight goes missing lets doctors pinpoint where along the pathway the trouble lies, even without looking inside the skull.