ametropia vs visual defect

ametropia and visual defect both are nouns.

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

As nouns, visual defect is a hypernym of ametropia; that is, visual 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
visual defect: impairment of the sense of sight

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

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