opto-

Opto- is a combining form used like a prefix meaning “optic” or “vision.” It is often used in scientific and medical terms, especially in optometry and ophthalmology.

Opto- comes from the Greek optós, meaning “visible.” This word is related to the Greek word ṓps, meaning “eye” or “face,” and ophthalmós, meaning “eye.” Ophthalmós is ultimately the source of ophthalmo- and ophthalm-. Also ultimately coming from the Greek ṓps are the combining forms -opia, -opsia, -opsy, and -opy.

The Latin word for “eye” is oculus, source of the combining form oculo-.

What are variants of opto-?

When combined with words or word elements that begin with a vowel, opto- becomes opt-, as in optesthesia.

An example of a word you may have encountered that features the combining form opto- is optometry, “the practice or profession of examining the eyes.”

We know that opto- means “vision,” but what about the -metry part of the word? The combining form -metry means “the process of measuring.” Optometry literally translates to “measuring vision.”

What are some words that use the combining form opto-?

• optotype
• optometer
• optophone
• optokinetic
• optoelectronics

What are some other forms that opto- may be commonly confused with?

• octo-
• onto-
• oto-

Not every word that begins with the exact letters opto- or opt- are necessarily using the combining form opto- to denote “vision,” such as optimal. Learn why optimal means “best” at our entry for the word.

The combining form -meter means “measure” and is used in the names of various measuring instruments. An optometer is an instrument used to make a special type of measurement on what part of the body?