nyctalopia vs visual disorder

nyctalopia and visual disorder both are nouns.

Word	Noun	Adjective	Verb	Adverb
nyctalopia	Yes	No	No	No
visual disorder	Yes	No	No	No

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

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

Other hypernyms of nyctalopia include avitaminosis, hypovitaminosis, vision defect, visual defect, visual impairment.

nyctalopia (noun)	visual disorder (noun)
inability to see clearly in dim light; due to a deficiency of vitamin A or to a retinal disorder	impairment of the sense of sight