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1 Central anatomy of the IVth nerveThe IVth or trochlear nucleus is located ventral to the central periaqueductal grey matter, dorsal to the medial longitudinal fasciculus (MLF) and medial to the oculosympathetic tract at the level of the inferior colliculus. The fascicles of the IVth nerve travel dorsally and caudally around the cen...
2 Brainstem ocular motor machinerySeen here is a sagittal view of the brainstem. The medulla has a significant role in gaze-holding, and the nucleus prepositus hypoglossi (NPH, along with the medial vestibular nucleus ) is the horizontal neural integrator. The abducens (6th) nucleus is located in the dorsal pons, and sends off the 6...
3 Medullary structures relevant to upbeat nystagmusThis is an axial section of the medulla, slightly more caudal as compared to (please refer to figure "medullary structures relevant to the ocular motor and vestibular consequences of the lateral medullary (Wallenberg) syndrome). Again seen are the inferior cerebellar peduncle (ICP) and caudal aspect...
4 Coronal section of the brainstem showing ocular motor nuclei and anatomy of the vestibular nucleus (with SCC inputs)(A) Seen here is a coronal view of the brainstem showing the locations of the ocular motor nuclei (IIIrd, IVth, VIth) as well as the nuclei of VII and VIII (vestibular and cochlear). The vestibular nucleus (VN) is divided into the inferior, lateral, medial, and superior subnuclei, and the medial ves...
5 Eyelid anatomySeen here are the major muscles of eyelid opening and closure. The levator palpebrae, which is innervated by the oculomotor nerve, inserts on the tarsus via the levator aponeurosis and directly on the skin of the upper eyelid. The superior tarsal muscle (also known as Muller's muscle, which is inner...
6 Medullary structures relevant to the ocular motor and vestibular consequences of lateral medullary (Wallenberg) syndromeThis is an axial section of the medulla showing the structures that, when damaged, are responsible for the vestibular and ocular motor features of the lateral medullary or Wallenberg syndrome. The nucleus prepositus hypoglossi (NPH) and medial vestibular nucleus (MVN) complex is important for horizo...
7 Central anatomy of the IIIrd nerveSeen here is an axial section of the midbrain at the level of the superior colliculus. The paired nuclei are located ventral to the periaqueductal grey, and the midline central caudal nucleus (CCN) is located between the right and left nuclei. The CCN sends projections to bilateral levator palpebrae...
8 Sagittal section of the brainstem showing structures related to normal eyelid functionSeen here is a sagittal view of the brainstem, with the structures relevant to normal eyelid function highlighted. The M-group, which can be found medial to the riMLF (coordinates eye and lid movements), has (weak) projections to the facial nucleus for frontalis muscle contraction, and (strong) proj...
9 Sagittal section of the midbrain showing structures related to normal eyelid functionDuring a vertical saccade, the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) is activated, which excites the superior rectus (SR) and inferior oblique (IO) (IIIrd nerve) subnuclei. Additionally, the riMLF activates the nearby M-group. The M-group's primary excitatory out...
10 Relationship between semicircular canals and extraocular musclesFigure 1: When stimulated, each of the 6 angular acceleration detecting semicircular canals (3 on the right and 3 on the left) responds with a conjugate eye movement, with the vector(s) indicated below. PC=posterior canal; HC=horizontal (also known as lateral) canal; AC=anterior (also known as super...
11 Using video head impulse testing to unmask covert saccades in compensated vestibular neuritis - Figures 1 and 2This is a 30-year-old woman who experienced the acute vestibular syndrome (prolonged vertigo for >24 hours, nausea, unsteadiness, spontaneous nystagmus, head motion intolerance) and was diagnosed with vestibular neuritis. This diagnosis was based on a positive head impulse test to the left (see Figu...
12 Pons: 6th, 7th, 8th, and middle cerebellar peduncle anatomyFrom this cross-section of the pons, the proximity of the 7th and 8th fascicles can be appreciated, and a lateral inferior pontine syndrome (anterior inferior cerebellar artery territory), which could involve both of these fascicles, could cause acute prolonged vertigo accompanied by a + ipsilateral...
13 Pons: 6th and 7th nerve anatomy and the central tegmental tractFrom this cross-section of the pons, the proximity of the 6th nucleus to the 7th nerve fascicles is apparent. This is the basis of the so-called facial colliculus syndrome, where an ipsilesional horizontal gaze palsy from a nuclear 6th lesion (usually related to stroke or demyelination) can be seen ...
14 Periodic alternating nystagmus due to nodulus stroke - Figure 1This is a 70-year-old woman who experienced the acute onset of vertigo and imbalance. MRI demonstrated a diffusion-weighted imaging hyperintensity involving the nodulus (with corresponding ADC hypointensity) consistent with an acute stroke. On examination several weeks after the stroke, periodic alt...
15 Saccadic pathways in the brainstem and cerebellum & mechanism for saccadic dysmetria in Wallenberg syndrome - Normal function of the brainstem/cerebellar saccadic pathwaysThe inferior cerebellar peduncle (ICP) carries climbing fibers to the dorsal vermis, and these fibers have an inhibitory influence over the Purkinje cells. These Purkinje cells normally inhibit the ipsilateral fastigial nucleus, and the fastigial nucleus projects to the contralateral inhibitory burs...
16 Ocular motor & vestibular features of the MLF syndrome - Figures 1, 2, and 3This 61-year-old woman with HTN and DM presented for evaluation of acute onset diagonal diplopia. Adduction OS was about 60% of normal while medialization OS improved with convergence. In right gaze, dissociated abducting nystagmus was present OD, and there was a clear adduction lag when asking he...
17 Oculopalatal tremor with prominent nystagmus, bilateral horizontal gaze palsy, and bilateral facial palsies Figure 1Figure 1, MRI T2 sequence demonstrating hyperintensities involving bilateral inferior olives of the medulla. This is a 50-year-old woman who experienced the acute onset of right sixth and seventh nerve palsies and left hemiparesis. Two cavernomas within the right pons (one in the region of the facia...
18 A Comparison of Nystagmus and Saccadic Intrusions/OscillationsNystagmus can be classified into pendular and jerk waveforms, where both are generated by a slow, pathologic phase. Corrective phase (the position reset mechanism) differs. In pendular nystagmus, the eyes move back and forth with about the same velocity and amplitude, similar to that of a pendulum...
19 Vestibular neuritis with + head impulse test and unidirectional nystagmus-Figure 1Vestibular neuritis is the most common cause of the acute vestibular syndrome, which is characterized by continuous vertigo and spontaneous nystagmus lasting days. It may be mimicked by central causes, including stroke, but in the hands of subspecialists, the HINTS+ (Head Impulse, Nystagmus, Test of...
20 Neuro-ophthalmic features and pseudo-MG lid signs in Miller Fisher syndrome - Figure 1This is a 51-year-old woman who presented with imbalance, acute onset dizziness and diplopia that developed over three days following two weeks of upper respiratory infection and bacterial conjunctivitis. When she was initially seen as an outpatient, nystagmus was noted to the right and left, and a ...
21 Triangle of Guillain-MollaretSeen here is a schematic representation of the Gullain-Mollaret triangle (Figure 1), also referred to as the dentato-olivary pathway, reflecting the 3 points of this imaginary triangle - 1) dentate nucleus, 2) red nucleus, and 3) inferior olivary nucleus. The olive sends decussating climbing fibers ...
22 Subtle torsional pendular nystagmus in oculopalatal tremor (OPT) - Figure 1This is a 50-year-old woman who presented with imbalance, and MRI demonstrated a right cerebellar cavernous malformation. She underwent surgery to resect the malformation, and post-operatively experienced right hemiparesis and ataxia. Six months after the surgery, balance worsened and vision became ...
23 Saccadic pathways in the brainstem and cerebellum & mechanism for saccadic dysmetria in Wallenberg syndrome - Abnormal function of the brainstem/cerebellar saccadic pathways with a left Wallenberg syndromeThe end result of a lesion involving the climbing fibers within the left lateral medulla is deficient rightward saccades (contralesional hypometric saccades), and over-active leftward saccades (ipsilesional hypermetric saccades), and ipsilesional ocular lateropulsion given this baseline imbalance. M...
24 The utriculo-ocular motor pathways - physiologic and pathologic ocular tilt reaction: Physiologic ocular tilt reaction (OTR) (Figure 1)A skew deviation is a non-paralytic vertical ocular misalignment that is due to imbalance in the utriculo-ocular motor pathways. While vestibular jerk nystagmus is a consequence of static semicircular canal pathway imbalance (e.g., left-beating nystagmus due to acute right vestibular hypofunction fr...
25 The utriculo-ocular motor pathways - physiologic and pathologic ocular tilt reaction: OTR Diagram Pathologic EOMs Labelled (Figure 3)A skew deviation is a non-paralytic vertical ocular misalignment that is due to imbalance in the utriculo-ocular motor pathways. While vestibular jerk nystagmus is a consequence of static semicircular canal pathway imbalance (e.g., left-beating nystagmus due to acute right vestibular hypofunction fr...
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