| Chapter 15 Concomitant Vertical Deviations PAUL R. MITCHELL and MARSHALL M. PARKS Table Of Contents |
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SKEW DEVIATION REFERENCES |
| 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.1–10 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. Concomitant vertical and horizontal deviations are common. Therapy directed at both is ideal, for example, plus lenses for the accommodative esodeviation, which may be displaced in the spectacle frame to obtain vertical correction or incorporation of vertical prism power with the spheric or spherocylindric power. Patients with relatively large deviations requiring operative intervention should have simultaneous surgical procedures on one horizontal and one vertical rectus muscle in each eye. Symmetric surgery is performed on the vertical and horizontal muscles to overcome the esotropia or exotropia combined with concomitant right or left hypertropia. Concomitant vertical strabismus secondary to prior extraocular muscle surgery may be due to many causes. Correction requires determining the specific cause and surgically eliminating it. |
| SKEW DEVIATION |
| Hypertropia that is not resulting from the usual causes and is associated
with a central nervous system disorder or labyrinthitis should be suspected
as being skew deviation. The onset is abrupt, and the vertical
deviation is usually large and variable. Skew deviation can simulate
almost any type of vertical misalignment. It may be constant in all positions of gaze or there may be right hypertropia
in one lateral gaze and left hypertropia in the other. Skew deviation
may so closely resemble a palsy of a cyclovertical muscle that
an erroneous diagnosis can be prevented only by keeping the diagnosis
of skew deviation in mind when there is an associated neurologic abnormality. Trobe12 states that skew deviation is not associated with a cyclo component, which
assists in the differentiation from the cyclovertical deviation character
of fourth cranial nerve palsy. Kushner13 has noted that the third step of the Parks three-step test does
not invariably define whether one is dealing with a palsy of a single
cyclovertical muscle. Because other causes of vertical strabismus such
as skew deviation, myasthenia gravis, dissociated vertical deviations, prior
vertical eye muscle surgery, contracture of vertical rectus muscles, paresis
of more than one vertical muscle, and small nonparalytic
vertical deviations associated with horizontal strabismus may have a
positive Bielschowsky head tilt test as well, the use of the three-step
test may lead to incorrect diagnosis and treatment in these
conditions. Kushner13 recommends additional diagnostic steps, beyond the three-step test, including
testing for the presence of a secondary deviation, especially
if the visual acuity is unequal; assessing ocular rotations of
both eyes in the diagnostic fields of gaze; qualitative cover testing
in the oblique fields of gaze; determining if the hypertropia is dissociated; obtaining
histories of previous surgery; and history or clinical
findings to suggest a skew deviation or myasthenia gravis. Donahue
and co-workers14 concluded that although many vertical deviations appear to be due to inferior
oblique palsy based on the results of the three-step test
with inferior oblique weakness or palsy, skew deviation should also
be considered in any patient with a history of head trauma or other neurologic
findings. According to Cogan,15 skew deviation is most commonly associated with lesions of the cerebellum, brain stem, and labyrinth. The usual etiologic agents are cerebellar tumors and abscesses, acoustic neuromas, vascular lesions of the pons and cerebellum, and cerebellar herniations into the foramen magnum complicating platybasia. Skew deviation is rarely associated with demyelinating diseases. Skew deviation is more common in unilateral intracranial lesions than in bilateral lesions. Characteristically, if internuclear ophthalmoplegia were an associated finding, the cranial lesion would be unilateral and not bilateral. Miller16 states that when skew deviation is associated with internuclear ophthalmoloplegia, the higher eye is usually on the side of the intracranial lesion. However, Cogan15 states that the eye on the side of the intracranial lesion usually is hypotropic. Skew deviation disappears once the etiologic factor is removed. Brandt and Dieterich17 described three different types of skew deviation when occurring as a manifestation of ocular tilt reaction. In type 1, there is upward deviation of both eyes with different amplitudes (utricle type, vestibular symptoms with perilymph fistulas); in type 2, there is hypertropia of one eye while the other eye remains in the primary position (dorsolateral medulla oblongata infarctions, Wallenberg syndrome); and in type 3, there is simultaneous hypertropia of one eye and hypotropia of the other eye (as described for electrical stimulation of midbrain tegmentum in monkeys and in humans with paroxysmal ocular tilt reaction secondary to upper brainstem lesions such as multiple sclerosis or brain abscess). In a subsequent report, Brandt and Dieterich18 suggest that the most likely hypothetical mechanism for skew deviation is that it results from unilateral damage of the tonic otolith-ocular pathways or the pathways mediating the vestibuloocular reflex (VOR) in the roll plane. In their study of 56 patients with unilateral brain stem infarctions presenting with skew deviation, they found that all skew deviations were ipsiversive (ipsilateral eye was undermost) with caudal pontomedullary lesions, and contraversive (contralateral eye was lowermost) with rostral pontomesencephalic lesions, and that all skew deviations were associated with concomitant ocular torsion and tilts of subjective visual vertical toward the lowermost eye. Skew deviation, or ocular skew torsion is a sensitive brain stem sign of localizing and lateralizing value. |