sightlessness vs anopia

sightlessness and anopia both are nouns.

Word	Noun	Adjective	Verb	Adverb
sightlessness	Yes	No	No	No
anopia	Yes	No	No	No

As nouns, anopia is a hyponym of sightlessness; that is, anopia is a word with a more specific, narrower meaning than sightlessness:

sightlessness: the state of being blind or lacking sight
anopia: sightlessness (especially because of a structural defect in or the absence of an eye)

Other hyponyms of sightlessness include legal blindness, snow-blindness, snowblindness, eyelessness, figural blindness.

sightlessness (noun)	anopia (noun)
the state of being blind or lacking sight	sightlessness (especially because of a structural defect in or the absence of an eye)