If you describe something as optic, it has something to do with eyes or vision. Your optic nerve, for example, sends information to your brain from your eyes.
You'll most often find the adjective optic in anatomy or biology textbooks, describing the parts of an eye, or disorders involving the eye. Your optic disc is a tiny blind spot that all humans have on their eyeballs, and optic neuritis is an inflammation of the optic nerve. When it's a noun, optic is an old-fashioned, jokey way to say "eyeball." Optic comes from the Greek optikos, "of or having to do with sight."