hemianopsia vs vision defect

hemianopsia and vision defect both are nouns.

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

As nouns, vision defect is a hypernym of hemianopsia; that is, vision defect is a word with a broader meaning than hemianopsia:

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

hemianopsia (noun)	vision defect (noun)
blindness in one half of the visual field of one or both eyes	impairment of the sense of sight