Concomitant vertical misalignment of a few diopters is not a rare occurrence. In most instances, good fusional vergences overcome the deviation, resulting in fusion. The best test to elicit small vertical phorias is the Maddox rod in which the patient fixates on a small, point source of light first at a distance and then nearby. The quantity of deviation is measured with the Maddox rod and prism, and the vertical vergence amplitude is determined. Treatment of the vertical error is justified according to the magnitude of the deviation and the symptoms it provokes. Vertical vergence amplitude training by orthoptics usually does not produce improvement. Compensating for a portion or all of the vertical deviation with prism correction in spectacles is often helpful in deviations below 10Δ.

Large primary concomitant vertical deviations not secondary to previous extraocular muscle surgery are rare. The primary concomitant vertical deviation must be differentiated from skew deviation, which is rather abrupt in onset, variable, and associated with symptoms caused by intracranial or labyrinthian disease.

Orbital asymmetry associated with facial and cranial bone disorders can cause a vertical strabismus, but more often the physician is surprised to find an absence of deviation of the eyes in the presence of a large vertical asymmetry of the orbits. Generally, the hypertropic eye in plagiocephaly is on the side with the twisted orbit caused by the cranial dysostosis.

Vertical and cyclotorsional deviations have been described after local anesthesia for cataract surgery.^{1,2,3,4,5,6,7,8,9,10} Suggested etiologies have included underaction of extraocular muscles secondary to hemorrhage or mechanical trauma with extraocular muscle atrophy, traumatic neuroparesis, toxic side effects of anesthesia, or secondary fibrosis of the extraocular muscles. In the series reported by Neugebauer and co-workers,¹¹ using the Bielschowsky head tilt test, all patients described binocular diplopia, all had hypotropia of the involved eye, and all had no significant enlargement of the vertical angle to either side. However, in contrast to primary comitant vertical deviations, all patients had increase in the vertical angle of deviation in downgaze, in both adduction and abduction. All traction tests intraoperatively demonstrated restricted inferior rectus function.

The recession procedure on a vertical rectus muscle of each eye is the best treatment: one muscle has its vertical action in right gaze and the other in left gaze; one muscle is an elevator and the other is a depressor. A recession of both appropriate vertical rectus muscles to overcome 15Δ to 25Δ of hypertropia generally provides symmetric improvement in dextroversion, levoversion, supraversion, and infraversion to the same degree as the improvement in the primary position. For 15Δ of concomitant hypertropia a 3 mm recession on each vertical rectus muscle is performed; for 20Δ, a 3.5 mm recession and for 25Δ, a 4 mm recession.