aphakia vs visual impairment

aphakia and visual impairment both are nouns.

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

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

aphakia: absence of the natural lens of the eye (usually resulting from the removal of cataracts)
visual impairment: impairment of the sense of sight

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

aphakia (noun)	visual impairment (noun)
absence of the natural lens of the eye (usually resulting from the removal of cataracts)	impairment of the sense of sight