moon blindness vs visual defect

moon blindness and visual defect both are nouns.

Word	Noun	Adjective	Verb	Adverb
moon blindness	Yes	No	No	No
visual defect	Yes	No	No	No

As nouns, visual defect is a hypernym of moon blindness; that is, visual defect is a word with a broader meaning than moon blindness:

moon blindness: inability to see clearly in dim light; due to a deficiency of vitamin A or to a retinal disorder
visual defect: impairment of the sense of sight

Other hypernyms of moon blindness include avitaminosis, hypovitaminosis, vision defect, visual disorder, visual impairment.

moon blindness (noun)	visual defect (noun)
recurrent eye inflammation in horses; sometimes resulting in blindness	impairment of the sense of sight
inability to see clearly in dim light; due to a deficiency of vitamin A or to a retinal disorder