opto- Also opti-.
[Greek optos, seen.]
Optometry is the occupation of measuring eyesight, prescribing corrective lenses, and detecting eye disease. The form appears in a few terms relating to the use of light in electronics, especially optoelectronics (or optronics), the branch of technology concerned with the inter-conversion of electronics and light; and optocoupler, a device containing light-emitting and light-sensitive components, used to couple isolated circuits.
Words in opti- come from Latin opticus or optica, which derive from the same Greek source. Examples are optic and optical, of or relating to the eye or vision; optics, the scientific study of sight and the behaviour of light; and optician, a person qualified to prescribe and dispense glasses and contact lenses, and to detect eye diseases.