visual defect vs visual impairment

visual defect and visual impairment both are nouns.

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

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

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

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