optometrist vs specializer

optometrist and specializer both are nouns.

Word	Noun	Adjective	Verb	Adverb
optometrist	Yes	No	No	No
specializer	Yes	No	No	No

As nouns, specializer is a hypernym of optometrist; that is, specializer is a word with a broader meaning than optometrist:

optometrist: a person skilled in testing for defects of vision in order to prescribe corrective glasses
specializer: an expert who is devoted to one occupation or branch of learning

Other hypernyms of optometrist include specialiser, specialist.

optometrist (noun)	specializer (noun)
a person skilled in testing for defects of vision in order to prescribe corrective glasses	an expert who is devoted to one occupation or branch of learning