Correct Answer: Ophthalmologist

Solution : The correct answer is the first option.

The most appropriate 'one word' for the expression "one who cures eye disease" is ophthalmologist . This term is derived from the Greek words "ophthalmos" (meaning "eye") and "logos" (meaning "study" or "science"). An ophthalmologist is a medical doctor who specialises in the diagnosis and treatment of eye diseases and disorders.

The meanings of the other options are as follows:

Prologist: This term doesn't have a specific meaning related to eye diseases.

Phonologist: A phonologist is someone who studies the sound systems of languages, particularly in linguistics. This term is not related to curing eye diseases.

Biologist: A biologist is a scientist who studies living organisms and their interactions. This term is not specific to eye diseases.

Therefore, the correct word is opthalmologist.