optometrist vs specialiser

optometrist and specialiser both are nouns.

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

As nouns, specialiser is a hypernym of optometrist; that is, specialiser 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
specialiser: an expert who is devoted to one occupation or branch of learning

Other hypernyms of optometrist include specialist, specializer.

optometrist (noun)	specialiser (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