A 10-year-old German girl's perfect vision baffled doctors - because she was born with only the left hemisphere of her brain. Humans with both hemispheres see because visual information delivered by the optic nerves cross over to the opposite hemisphere for processing and storage. So, one brain hemisphere should mean that only one eye works; in the girl's case, only her right eye should work.
Yet, the girl enjoys normal, binocular vision and in 2010, doctors scanned her brain to determine why. It turned out that through a process called plasticity, the optic nerve from her left eye had migrated to her left hemisphere; in other words, the left side of the girl's brain was accepting visual information from both eyes.
Astoundingly, the visual cortex on her left hemisphere had developed areas set aside for processing information from the left eye, which avoided confusion [source: PhysOrg].