An elevation of the adducted eye in the absence of a significant hypertropia in primary position is commonly referred to as an upshoot in adduction. It is fallacious to believe that every apparent overaction in the field of action of the inferior oblique muscles is, in fact, an overaction of that muscle. Failure to recognize that a variety of different conditions may produce a clinical picture of often remarkable similarity may lead to the wrong diagnosis and the wrong therapy.The first step in analyzing the problem is to observe and then to measure whether the elevation is limited to adduction or exists in other gaze positions as well. Special attention should be paid to any other overacting or, perhaps, underacting muscles as the patient maintains fixation with either eye in the diagnostic positions of gaze.

In SO palsy the upshoot in adduction caused by a secondary overaction of the inferior oblique muscle. This muscle is unopposed by its paretic antagonist. This difference in vertical deviation on tilting the head to the right and left shoulder (Bielschowsky test ). In primary overaction of the inferior oblique muscle, the function of the superior oblique is usually normal. The condition is often bilateral and accompanied by a V pattern esotropia in a downward gaze. Unlike in bilateral superior oblique paralysis, the Bielschowsky test is negative.

Surgical treatment of primary IO overaction is myectomy of these muscles