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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 �DZ��ó��, meaning “visible.” This word is related to the Greek word ����, meaning “eye” or “face,” and �DZ��ٳ󲹱���ó��, meaning “eye.” �����ٳ󲹱���ó�� is ultimately the source of ophthalmo- and ophthalm-. Also ultimately coming from the Greek ���� 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?