hemeralopia vs vision defect

hemeralopia and vision defect both are nouns.

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

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

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

hemeralopia (noun)	vision defect (noun)
inability to see clearly in bright light	impairment of the sense of sight