Select the most appropriate 'one word' for the expression given below.

One who cures eye disease.

Ophthalmologist

The most appropriate one-word substitute for "one who cures eye disease" is ophthalmologist.

• Ophthalmologist is a medical doctor who specializes in the eyes and vision.
• Prologist is a medical doctor who specializes in the prostate gland.
• Phonologist is a linguist who studies the sound system of a language.
• Biologist is a scientist who studies living things.

Ophthalmologist is the most appropriate word for the given expression because it specifically refers to a doctor who treats eye diseases. It is derived from the Greek words ophthalmos, meaning "eye," and logos, meaning "study of."