What do you call someone who is good at their job? For example: how would you describe an optometrist/ophthalmologist who is really good at what they do?
Expert—either as a noun:
Or as an adjective:
Having or involving authoritative knowledge [ODO]
having or showing special skill or knowledge because of what you have been taught or what you have experienced [M-E]
A couple of mildly informal adjectives for describing exceptional competence are crack and crackerjack:
- Highly trained and competent. Even a crack team of investigators would have trouble solving this case.
- Excellent, first-rate, superior, top-notch. She's a crack shot with that rifle.
- Exceptionally fine or excellent; top-notch; high quality.
- Expert, top-rated or high-performing.
An example from an Ngram search:
I had an able staff in the District of Columbia Committee and with personnel like Mr. Malone, who came to us from the city government, and there was a crackerjack lawyer who was completely devoted to doing his job in the District.
(Department of the Interior and related agencies appropriations for fiscal year 1970: Hearings before a subcommittee of the Committee on Appropriations, United States Senate, Ninety-first Congress, first session, on H.R. 12781, Part 1)
Professional is an appropriate way to refer to someone who is very competent in his job:
Worthy of or appropriate to a professional person; competent, skilful, or assured:
- his professional expertise their music is both memorable and professional
- a very professional optometrist/ophthalmologist.