metamorphopsia vs vision defect

metamorphopsia and vision defect both are nouns.

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

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

metamorphopsia: a defect of vision in which objects appear to be distorted; usually due to a defect in the retina
vision defect: impairment of the sense of sight

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

metamorphopsia (noun)	vision defect (noun)
a defect of vision in which objects appear to be distorted; usually due to a defect in the retina	impairment of the sense of sight