Loss of the normal paired movements of the eyes when tracking an object to the left or right. An INO is marked by the failure of one eye (e.g., the left) to cross the midline during an attempt to see an object on the opposite side of the body (e.g., the right).
A disturbance of coordinated eye movements in which the eye turned outward to look toward the side develops nystagmus (rapid, involuntary movements) while the other eye simultaneously fails to turn completely inward. This neurologic sign, of which the person is usually unaware, can be detected during the neurologic exam.