longsightedness vs ametropia

longsightedness and ametropia both are nouns.

Word	Noun	Adjective	Verb	Adverb
longsightedness	Yes	No	No	No
ametropia	Yes	No	No	No

As nouns, ametropia is a hypernym of longsightedness; that is, ametropia is a word with a broader meaning than longsightedness:

longsightedness: abnormal condition in which vision for distant objects is better than for near objects
ametropia: (ophthalmology) faulty refraction of light rays in the eye as in astigmatism or myopia

longsightedness (noun)	ametropia (noun)
abnormal condition in which vision for distant objects is better than for near objects	(ophthalmology) faulty refraction of light rays in the eye as in astigmatism or myopia