vision defect vs visual impairment

vision defect and visual impairment both are nouns.

Word	Noun	Adjective	Verb	Adverb
vision defect	Yes	No	No	No
visual impairment	Yes	No	No	No

As nouns, vision defect and visual impairment are synonyms defined as:

Other synonyms of vision defect include visual defect, visual disorder.

vision defect (noun)	visual impairment (noun)
impairment of the sense of sight	impairment of the sense of sight