ametropia vs visual impairment

ametropia and visual impairment both are nouns.

Word	Noun	Adjective	Verb	Adverb
ametropia	Yes	No	No	No
visual impairment	Yes	No	No	No

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

ametropia: (ophthalmology) faulty refraction of light rays in the eye as in astigmatism or myopia
visual impairment: impairment of the sense of sight

Other hypernyms of ametropia include vision defect, visual defect, visual disorder.

ametropia (noun)	visual impairment (noun)
(ophthalmology) faulty refraction of light rays in the eye as in astigmatism or myopia	impairment of the sense of sight