[Head-tilt test in unilateral and symmetric bilateral acquired trochlear nerve palsy]

BACKGROUND

The head-tilt phenomenon (difference between the vertical deviations with an ipsilateral and contralateral head-tilt by 45 deg. each) occurring in patients with a superior oblique palsy has traditionally been explained by the lacking contraction of the superior oblique muscle within the synkinetic movement of ocular counterrolling. However, using a computer model, Robinson showed that the superior oblique palsy itself causes only a relatively small head-tilt phenomenon. Adaptive mechanisms amplifying the otolith reflex were suggested to explain the increase of the head-tilt phenomenon in the course of time. In order to reduce the abnormal head posture required for binocular vision, the otolith reflex would be amplified, accepting the greater vertical deviation when the head is tilted to the paretic side .

QUESTION

If the head-tilt phenomenon were solely caused by the lacking contraction of the superior oblique muscle, it should be greater in bilateral than in unilateral superior oblique palsies. If an adaptive mechanism were acting to reduce the abnormal head posture, the head-tilt phenomenon should not be greater, and could even be smaller in bilateral than in unilateral superior oblique palsy, because in bilateral (symmetric) trochlear nerve palsies the vertical deviation at straight gaze is already small or absent without adaptation.

PATIENTS AND METHODS

We have carried out a retrospective comparison of 10 patients with bilateral symmetric superior oblique palsies and 10 patients with unilateral superior oblique palsy. In all cases, the palsy was acquired and had been present for at least 1 year.

RESULTS

The patients with bilateral superior oblique palsy had a head-tilt phenomenon ranging from 0 to 7 degrees (median, 2 deg.). The patients with unilateral superior oblique palsy had a head-tilt phenomenon between 2 and 13 degrees (median, 8 deg.). The difference was significant (p = 0.0117).

CONCLUSIONS

The head-tilt phenomenon is smaller in long-standing bilateral symmetric superior oblique palsies than in long-standing unilateral superior oblique palsy. This finding supports the hypothesis that in unilateral superior oblique palsy, an adaptive mechanism augments the head-tilt phenomenon by an amplification of the otolith reflex. However, we presume that the amplification of the otolith reflex is only a side effect of the adaptive change of the vertical fusional vergence tonus and thus the price of the improved vertical fusion, rather than a compensatory mechanism.

Anterior transposition of inferior oblique muscle for treatment of unilateral superior oblique muscle palsy with inferior oblique muscle overaction

Although many weakening procedures for the inferior oblique muscle have been advocated, there is some controversy as to the most beneficial procedure for weakening overacting inferior oblique muscles. This study was undertaken to determine if unilateral anterior transposition of the inferior oblique muscle alone could be a safe and effective procedure for treating unilateral superior oblique palsy from the perspective of hypertropia, inferior oblique overaction, and abnormal head posture. The records of 33 patients, who underwent anterior transposition of the inferior oblique muscle for unilateral superior oblique palsy at our institution between Jan 1995 and Dec 2002, were retrospectively reviewed. The average preoperative inferior oblique overaction was 2.3 +/- 0.64, and the hypertropia in the primary position was 12.3 +/- 7.69 prism diopter (PD). Twenty-six patients showed head tilt to the opposite direction preoperatively. After the anterior transposition of the inferior oblique, inferior oblique overaction was diminished in 32 patients (97%). Twenty-six out of 33 patients (79%) had no hypertropia in the primary position at last postoperative assessment. Of the 26 patients with head tilt before surgery, 21 patients (81%) achieved full correction after surgery. Satisfactory results were obtained in most of the patients in our study with the exception of three patients who required additional surgery. No patient demonstrated postoperative hypotropia in the primary position. None of the patients noticed elevation deficiency or lower lid elevation. The anterior transposition of the inferior oblique was found to be safe and effective for treating superior oblique palsy with secondary overaction of the inferior oblique muscle.

Ocular Rotation Axes during Dynamic Bielschowsky Head-Tilt Testing in Unilateral Trochlear Nerve Palsy

PURPOSE

To explain the positive Bielschowsky head-tilt (BHT) sign in unilateral trochlear nerve palsy (uTNP) by the kinematics of three-dimensional eye rotations.

METHODS

Twelve patients with uTNP monocularly fixed on targets on a Hess screen were oscillated (+/- 35 degrees, 0.3 Hz) about the roll axis on a motorized turntable (dynamic BHT). Three-dimensional eye movements were recorded with dual search coils. Normal data were collected from 11 healthy subjects.

RESULTS

The rotation axis of the viewing paretic or unaffected eye was nearly parallel to the line of sight. The rotation axis of the covered fellow eye, however, was tilted inward relative to the other axis. This convergence of axes increased with gaze toward the unaffected side. Over entire cycles of head roll, the rotation axis of either eye remained relatively stable in both the viewing and covered conditions.

CONCLUSIONS

In patients with uTNP, circular gaze trajectories of the covered paretic or unaffected eye during dynamic BHT are a direct consequence of the nasal deviation of the rotation axis from the line of sight. This, in turn, is a geometrical result of decreased force by the superior oblique muscle (SO) of the covered paretic eye or, according to Hering's law, increased force parallel to the paretic SO in the covered unaffected eye. The horizontal incomitance of rotation axes along horizontal eye positions can be explained by the same mechanism.

Incomitance of ocular rotation axes in trochlear nerve palsy

Strabismus due to palsy of a single muscle in one eye is always incomitant, which is a consequence of Hering's law of equal innervation. We asked whether this law had similar consequences on the orientation of ocular rotation axes. Patients with unilateral trochlear nerve palsy were oscillated about the nasooccipital (= roll) axis (+/-35 degrees, 0.3 Hz), and monocularly fixed on targets on a head-fixed Hess screen. Both the covered and uncovered eyes were measured with dual search coils. The rotation axis of the covered eye (paretic or healthy) tilted more nasally from the line of sight when gaze was directed toward the side of the healthy eye. The rotation axis of the viewing eye (paretic or healthy), however, remained roughly aligned with the line of sight. We conclude that incomitance due to eye muscle palsy extends to ocular rotation axes during vestibular stimulation.

Primary position and listing's law in acquired and congenital trochlear nerve palsy

PURPOSE

In ocular kinematics, the primary position (PP) of the eye is defined by the position from which movements do not induce ocular rotations around the line of sight (Helmholtz). PP is mathematically linked to the orientation of Listing's plane. This study was conducted to determine whether PP is affected differently in patients with clinically diagnosed congenital (conTNP) and acquired (acqTNP) trochlear nerve palsy.

METHODS

Patients with unilateral conTNP (n = 25) and acqTNP (n = 9) performed a modified Hess screen test. Three-dimensional eye positions were recorded with dual search coils.

RESULTS

PP in eyes with acqTNP was significantly more temporal (mean: 21.2 degrees ) than in eyes with conTNP (6.8 degrees ) or healthy eyes (7.2 degrees ). In the pooled data of all patients, the horizontal location of PP significantly correlated with vertical noncomitance with the paretic eye in adduction (R = 0.59). Using a computer model, PP in acqTNP could be reproduced by a neural lesion of the superior oblique (SO) muscle. An additional simulated overaction of the inferior oblique (IO) muscle moved PP back to normal, as in conTNP. Lengthening the SO and shortening the IO muscles could also simulate PP in conTNP.

CONCLUSIONS

The temporal displacement of PP in acqTNP is a direct consequence of the reduced force of the SO muscle. The reversal of this temporal displacement of PP, which occurs in some patients with conTNP, can be explained by a secondary overaction of the IO muscle. Alternatively, length changes in the SO and IO muscles, or other anatomic anomalies within the orbit, without a neural lesion, may also explain the difference in location of PP between conTNP and acqTNP.

Magnetic resonance imaging of the functional anatomy of the inferior oblique muscle in superior oblique palsy

PURPOSE

To study size and contractility of the normal inferior oblique (IO) muscle using high-resolution magnetic resonance imaging (MRI) and to evaluate abnormalities of the superior oblique (SO) and IO muscles in chronic SO palsy.

DESIGN

Prospective, case control study.

PARTICIPANTS

Thirteen patients with SO palsy and 17 orthotropic subjects.

METHODS

High-resolution, surface coil MRI was used to obtain sets of contiguous, 2-mm thick coronal and sagittal images repeated in multiple gaze directions. Digital image analysis was used to measure IO and SO muscle cross-sectional areas for evaluation of size and contractility. Diagnosis of SO palsy in one bilateral and 12 unilateral cases was based on subnormal contractility and SO size less than the normal 95% confidence limit. Ipsilesional and contralesional oblique muscles were compared with controls and correlated with clinical characteristics.

RESULTS

In all subjects, anterior movement and contractile thickening of the IO were observed in supraduction, with posterior movement and relaxational thinning in infraduction. The mean (+/- standard deviation) cross-sectional area of 15 normal control IO muscles was 13.4 +/- 3.9 mm(2), with mean contractile increase from infraduction to supraduction of 5.7 +/- 2.6 mm(2). Subjects with SO palsy had incomitant hypertropia with a wide range of overelevation and underelevation in adduction (i.e., upshoot, downshoot). SO atrophy correlated with underdepression in adduction (P < 0.0001). Contralesional SO cross-section was slightly greater than normal (P = 0.004). The IO cross-section ipsilesional and contralesional to SO palsy did not, however, differ significantly from normal and did not correlate with elevation in adduction (P > 0.2).

CONCLUSIONS

Quantitative morphometry by MRI can demonstrate IO size and contractility. Even in cases of unequivocal SO palsy associated with ipsilesional SO atrophy and deficient contractility, the degree of elevation in adduction was not correlated with IO size. This finding suggests that the associated overelevation in adduction, commonly termed "inferior oblique overaction," actually arises from some other mechanism than IO hypertrophy or excess contractility. Revision of clinical terminology seems warranted.

Three-dimensional eye movement analysis of superior oblique myokymia

PURPOSE

To confirm the idea that sole contraction of the superior oblique muscle causes attacks of superior oblique myokymia (SOM).

DESIGN

Observational case report.

METHODS

A 43-year-old man presented with episodic monocular oscillatory eye movements. Three-dimensional eye movements were recorded using the magnetic search coil system and analyzed as rotation vector. The attacks of SOM consisted of intorsional, depressive, and abductive fast phases and their exponential decaying slow phases.

RESULTS

Average direction of rotation axis for the fast phases while fixating straight ahead was 51.5 +/- 5.4 degrees from depression axis in vertical-torsional plane, 78.7 +/- 4.4 degrees from abduction axis in horizontal-torsional plane, and 76.3 +/- 4.3 degrees from abduction axis in horizontal-vertical plane (+/-SD, n = 50). Time constants of slow phases were less than 0.1 second.

CONCLUSIONS

Quantitative three-dimensional analysis of SOM directly confirmed that the fast phases of SOM attacks were induced by the sole contraction of the superior oblique muscle.

[Myokymia of the obliquus superior muscle and cryptogenetic epilepsy]

BACKGROUND

Myokymia of the obliquus superior muscle is a rare episodic microtremor caused by uncontrolled activities of the trochlearis nerve fibres. Epilepsy is also caused by spontaneous discharges of neurons. In our report we present an associated epilepsy which to the best of our knowledge is described for the first time.

PATIENT

An 61-year old man with twitches of the right eye for 6 weeks and a subjective feeling of eye movement was investigated at our hospital. His history was void of any ophthalmologic diseases. However, he suffered from cryptogenetic epilepsy known since childhood. The morphological and orthoptical findings of his eyes were normal. During the slit-lamp investigation a unilateral rotating microtremor of the right eye induced by looking downward was seen. The neurologic investigation, magnetic resonance imaging and assessment of the thyreoid function did not show further pathological results. The patient underwent treatment with carbamazepine. Under this therapy he did not show any symptoms of myokymia during follow-up.

SUMMARY

To the best of our knowledge this is the first case of myokymia of the obliquus superior muscle associated to epilepsy. To our opinion, any case of this syndrome should be investigated for epilepsy. A causal relation is unlikely since the most probable etiologies are either spontaneous discharges of trochlear nucleus neurons or a close contact between vessel and nerve analogously to trigeminal neuralgia.

Contribution of vergence adaptation to difference in vertical deviation between distance and near viewing in patients with superior oblique palsy

PURPOSE

To evaluate the adaptive vertical vergence aftereffect and determine whether it contributes to a difference of vertical deviation with respect to gaze distance in patients with vertical strabismus.

DESIGN

Prospective noncomparative studies.

METHODS

Eighty-four patients with unilateral superior oblique palsies were enrolled and classified into three types-A, B, and C-based on the difference in vertical deviation between distant and near viewing. The prism adaptation test was performed for 2 to 3 hours to correct vertical deviation and the response of vertical deviation to the prism adaptation test was compared among the three types

RESULTS

Adaptive vertical vergence aftereffect, defined as an increase of deviation by 5 prism diopters or more with the prism adaptation test, was identified in 13 patients (16%) at distance and in 23 patients (27%) at near viewing. Among the three types, the adaptive vergence aftereffect contributed mostly to the type B, in which distance deviation exceeds near deviation. Nine patients (39%) of type B changed to type A category with the prism adaptation test; and of these, 7 increased near deviation so that the deviation difference between distant and near viewing decreased.

CONCLUSION

The adaptive vertical vergence aftereffect contributes to a difference in vertical deviation between distant and near viewing. The vertical prism adaptation test is specifically useful to determine the extent of surgery by breaking fusional vergence in patients with hypertropia in whom deviation differs with respect to viewing distance.

The vestibulo-ocular reflex in fourth nerve palsy: deficits and adaptation

The effects of fourth nerve palsy on the vestibulo-ocular reflex (VOR) had not been systematically investigated. We used the magnetic scleral search coil technique to study the VOR in patients with unilateral fourth nerve palsy during sinusoidal head rotations in yaw, pitch and roll at different frequencies. In darkness, VOR gains are reduced during incyclotorsion, depression and abduction of the paretic eye, as anticipated from paresis of the superior oblique muscle. VOR gains during excyclotorsion, elevation and adduction of the paretic eye are also reduced, whereas gains in the non-paretic eye remain normal, indicating a selective adjustment of innervation to the paretic eye. In light, torsional visually enhanced VOR (VVOR) gains in the paretic eye remain reduced; however, visual input increases vertical and horizontal VVOR gains to normal in the paretic eye, without a conjugate increase in VVOR gains in the non-paretic eye, providing further evidence of selective adaptation in the paretic eye. Motions of the eyes after fourth nerve palsy exemplify monocular adaptation of the VOR, in response to peripheral neuromuscular deficits.

Adaptive neural mechanism for listing's law revealed in patients with fourth nerve palsy

PURPOSE

During fixation and saccades, human eye movements obey Listing's law, which specifies the eye's torsional angle as a function of its horizontal and vertical position. Torsion of the eye is in part controlled by the fourth nerve. This study investigates whether the brain adapts to defective torsional control after fourth nerve palsy.

METHODS

Thirteen patients with fourth nerve palsy (11 chronic, 2 acute), and 10 normal subjects were studied with scleral search coils. With the head immobile, subjects made saccades to a target that moved between straight ahead and eight eccentric positions. At each target position, fixation was maintained for 3 seconds before the next saccade. From the eye position data, we computed the plane of best fit, referred to as Listing's plane. Violations of Listing's law were quantified by computing the "thickness" of this plane, defined as the SD of the distances to the plane from the data points.

RESULTS

Both the paretic and nonparetic eyes in patients with chronic fourth nerve palsy obeyed Listing's law during fixation and saccades. However, Listing's planes in both eyes had abnormal orientations, being rotated temporally, meaning the eye excyclotorted during downgaze and incyclotorted during upgaze. In contrast, the paretic eye of patients with acute fourth nerve palsy violated Listing's law during saccades. During downward saccades, transient torsional deviations moved the paretic eye out of Listing's plane. Torsional drifts returned the paretic eye to Listing's plane during subsequent fixation.

CONCLUSIONS

During saccades, acute fourth nerve palsy violates Listing's law, whereas chronic palsy obeys it, indicating that neural adaptation can restore Listing's law by adjusting the innervations to the remaining extraocular muscles, even when one eye muscle remains paretic. The transient torsional deviations during downward saccades in acute palsy are attributed to pulse-step mismatch, as a result of lesions in the trochlear nerve that lead to an imbalance of phasic and tonic signals reaching the muscles.

Motor mechanisms of vertical fusion in individuals with superior oblique paresis

PURPOSE

We wanted to determine the mechanisms of motor vertical fusion in patients with superior oblique paresis and to correlate these mechanisms with surgical outcomes.

METHODS

Ten patients with superior oblique paresis underwent 3-axis, bilateral, scleral search coil eye movement recordings. Eye movements associated with fusion were analyzed.

RESULTS

Six patients had decompensated congenital superior oblique paresis and 4 had acquired superior oblique paresis. All patients with acquired superior oblique paresis relied predominantly on the vertical rectus muscles for motor fusion. Patients with congenital superior oblique paresis were less uniform in their mechanisms for motor fusion: 2 patients used predominantly the oblique muscles, 2 patients used predominantly the vertical recti, and 2 patients used predominantly the superior oblique in the hyperdeviated eye and the superior rectus in the hypodeviated eye. The last 2 patients developed the largest changes in torsional eye alignment relative to changes in vertical eye alignment and were the only patients to develop symptomatic surgical overcorrections.

CONCLUSION

There are 3 different mechanisms for vertical fusion in individuals with superior oblique paresis, with the predominant mechanism being the vertical recti. A subset of patients with superior oblique paresis uses predominantly the superior oblique muscle in the hyperdeviated paretic eye and the superior rectus muscle in the fellow eye for fusion. This results in intorsion of both eyes, causing a large change in torsional alignment. The consequent cyclodisparity, in addition to the existing vertical deviation, may make fusion difficult. The differing patterns of vertical fusional vergence may have implications for surgical treatment.

[Vertical vergence adaptation in cases of superior oblique palsy]

PURPOSE

To investigate the characteristics of vertical adaptation (VA) in superior oblique muscle palsy (SOP).

SUBJECTS AND METHODS

VA was examined in 15 patients with unilateral congenital SOP, 7 patients with unilateral acquired SOP, and 35 normal volunteers. An adaptive change in the fusion-free ocular alignment, VA, was measured with a computer-aided mirror haploscope. The fusion-free ocular alignment was measured before inserting a 3 prismdiopter vertical prism, immediately after inserting the prism, and at 10 minutes and 30 minutes after insertion. We investigated VA gain, age, vertical fusional range, response of prism adaptation test (PAT), and superior oblique muscle atrophy in magnetic resonance imaging (MRI).

RESULTS

The VA gain (mean +/- standard deviation, %) at 30 minutes in congenital, acquired, and normal groups was 86 +/- 53, 34 +/- 23 and 58 +/- 16, respectively. The mean of the VA gains at 30 minutes in the congenital group was greatest, and that in the acquired group was least(p < 0.01). In the congenital group there was a correlation between VA gain and response of PAT (p = 0.02, r = 0.60). The VA gain did not significantly correlate with age, vertical fusional range, or muscle atrophy.

CONCLUSION

The VA gain observed in congenital SOP was greater than that of acquired SOP, and affected the response of PAT.

Remission of superior oblique myokymia after microvascular decompression

Superior oblique myokymia (SOM) is an ocular motility disorder characterized by oscillopsia, vertical or torsional diplopia, sometimes combined with pressure sensation. Although the pathophysiological basis is unclear, isolated case reports have documented its association with intracranial pathological processes. We present a case of SOM associated with a vascular compression of the fourth nerve at the root exit zone. Following microneurosurgical decompression, SOM completely resolved and paralysis of the fourth nerve occurred. This was less disturbing.

Paralytic strabismus

In the last year, published works on paralytic strabismus have concerned many topics. New advances have been made in the knowledge of epidemiology of ocular nerve palsies in children, muscular causes of paralytic strabismus, and neuroimaging management of patients with third nerve palsy who are at risk of cerebral aneurysms. The author describes reports on rare associations of oculomotor imbalances and neurologic diseases as well as atypical orbital localizations of tumors. He also discuss new neuroimaging findings in congenital superior oblique muscle palsy and new acquisitions on cyclofusion deterioration in acquired trochlear palsy.

Cyclofusion in normal and superior oblique palsy subjects

PURPOSE

To evaluate the cyclofusional status in normal and acquired superior oblique palsy subjects. To know the extent to which cyclodeviations can be tolerated asymptomatically.

METHOD

Incyclovergence and excyclovergence break points and recovery points were evaluated in 40 normal subjects and 17 cases of acquired superior oblique palsy. A Polaroid dissociation stereoprojector was used with special torsional slides at fixation distances of 1 meter and 6 meters. In addition, maximum intorsion tolerated (MIT) and maximum extorsion tolerated (MET), ie, the torsion that allowed baseline horizontal fusion, were studied. The evaluation was repeated in the palsy group 1 month after recovery, which was spontaneous in 8 cases, and after surgery in 9 cases.

RESULT

The normal values for incyclovergence and excyclovergence were in the range of 12 degrees (break point) and 8 degrees (recovery point). In the case of superior oblique palsy, only the incyclovergence recovery point was significantly diminished (p=.004), which improved after recovery to near normal values. The intorsion tolerance (MIT) and extorsion tolerance (MET) also showed deterioration in the palsy group. After recovery, the MIT normalized but the MET did not recover at 1-meter distance fixation. The maximum torsional tolerance values appear to be more critical.

CONCLUSION

The cyclofusional vergence under physiological conditions are better than reported earlier. But MIT and MET are better indicators of cyclofusional potential. These low values demand more precise alignment of the torsion in weakening or strengthening surgery of the oblique muscles.

Neuroborreliosis and isolated trochlear palsy

We report here for the first time a child with isolated trochlear palsy and neuroborreliosis. IgG and IgM antibodies against Borrelia burgdorferi were highly positive in serum and cerebrospinal fluid respectively. The symptoms resolved completely after initiation of antibiotic treatment with ceftriaxone.

Bilateral recession of the superior oblique in "A" pattern tropia

A bilateral recession of an overacting superior oblique was performed in nine patients with "A" pattern ranging from 12 to 48 diopters, with an average of 24 prism diopters.There were six esotropic and three exotropic subjects. In all cases but one, some surgery of one or two horizontal recti was done at same time.An under correction was observed in two patients, of respectively 13 and 9 prism diopters. An overcorrection not exceeding 15 prism diopters was seen in six patients; in four it measured 3 prism diopters or less. A full correction was obtained in one case. The mean correction of "A" pattern was 25 prism diopters.Complications were not observed during the follow-up period.