Which root word relates to 'vision' in medical terminology?

The root word that relates to 'vision' in medical terminology is "optic/o." This root comes from the Greek word "optikos," which pertains to sight or vision. In medical terminology, it appears in words such as "optometry," the practice of measuring vision and prescribing corrective lenses, and "optic nerve," which is the nerve responsible for transmitting visual information from the retina to the brain.

The other root words provided do not relate to vision: "onc/o" refers to tumors, particularly in oncology; "onych/o" involves nails, commonly used in terms like "onychomycosis," a fungal nail infection; and "oophor/o" relates to the ovaries in the context of gynecology. Therefore, "optic/o" is the only root word specifically connected to vision.