What is the tertiary action of the inferior oblique?

• A. Depression
• B. Elevation
• C. Abduction
• D. Adduction

Answer: (C)

The inferior oblique primarily elevates the eye. Because its tendon inserts on the inferolateral sclera, its pull has a strong outward (temporal) component, which gives the eye an outward or abduction motion as part of its action. The elevation is the main effect, a secondary effect is extorsion (outward rotation), and the outward movement—abduction—is the tertiary action. So, when the eye is in the primary position, the muscle contributes mainly to lifting the eye and, to a lesser degree, moving it away from the midline. Abduction is the best choice because it represents that outward component of the inferior oblique’s action, beyond its primary elevation and secondary extorsion.