aphakia vs vision defect

aphakia and vision defect both are nouns.

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

As nouns, vision defect is a hypernym of aphakia; that is, vision defect 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)
vision defect: impairment of the sense of sight

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

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