dilatation vs mydriasis

dilatation and mydriasis both are nouns.

Word	Noun	Adjective	Verb	Adverb
dilatation	Yes	No	No	No
mydriasis	Yes	No	No	No

As nouns, mydriasis is a hyponym of dilatation; that is, mydriasis is a word with a more specific, narrower meaning than dilatation:

dilatation: the act of expanding an aperture
mydriasis: reflex pupillary dilation as a muscle pulls the iris outward; occurs in response to a decrease in light or certain drugs

Other hyponyms of dilatation include vasodilation.

dilatation (noun)	mydriasis (noun)
the act of expanding an aperture	reflex pupillary dilation as a muscle pulls the iris outward; occurs in response to a decrease in light or certain drugs
the state of being stretched beyond normal dimensions