optic disc vs optic disk

optic disc and optic disk both are nouns.

Word	Noun	Adjective	Verb	Adverb
optic disc	Yes	No	No	No
optic disk	Yes	No	No	No

As nouns, optic disc and optic disk are synonyms defined as:

optic disc and optic disk: the point where the optic nerve enters the retina; not sensitive to light

Other synonyms of optic disc include blind spot.

optic disc (noun)	optic disk (noun)
the point where the optic nerve enters the retina; not sensitive to light	the point where the optic nerve enters the retina; not sensitive to light