(optics) A disk of high-quality quartz glass having at least one side ground and polished with a deviation in flatness less than 50 nanometers all over, and a surface quality of 5 microfinish or less; used, in an interferometer, to measure the flatness of other surfaces.

plural of optical illusion

(neuroanatomy) Each of the second pair of cranial nerves that carry visual information from the retina to the brain.

Op art.

(telecommunications) A switch that can selectively change signals between optical fibers or integrated optical circuits.

(astronomy) A star that appears as a double due to an optical illusion; in reality, the stars may be far apart from each other.

That does not involve vision / That does not use optics

(physics) A device that employs a focused laser beam to trap, manipulate and image very small particles

Alternative spelling of optic disc

(anatomy) The location where ganglion cell axons exit the eye to form the optic nerve.