ametropia vs vision defect

ametropia and vision defect both are nouns.

Word	Noun	Adjective	Verb	Adverb
ametropia	Yes	No	No	No
vision defect	Yes	No	No	No

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

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

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

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