Fig. 1.

Summary of clinical findings, videooculography and neuroimaging. A Clinical neuroophthalmologic assessment shows a left hypertropia, rightward head deviation in the roll plane (ear to shoulder; dashed line approximation of a true horizontal, solid line approximation of patient’s actual head deviation) and esodeviation with right eye deviating inwards, greater on attempted upgaze. Vertical but not horizontal gaze range is limited. B Binocular videooculography. In darkness, the binocular vertical trace (light grey) shows a low frequency nystagmus with an upward directed quick phase and linear slow phase waveforms (highlighted in grey box I), co-occurring with a sparse convergent jerk (purple box) with following slow divergence visible in the horizontal trace. With fixation in light, the vertical and horizontal oscillations become significantly more intense and assume pendular waveforms (highlighted in grey box II and purple box). In left gaze, the horizontal oscillations are markedly attenuated, while vertical oscillations show a gaze-dependent shift of waveforms (highlighted in grey box III and IV). Vertical and horizontal oscillations are strongly correlated in both eyes. BIN V = binocularly averaged vertical trace, LE H = left eye horizontal, RE H = right eye horizontal. C MR-imaging (4 mm isotropic) acquired in the acute setting reveals a solitary, 3.8 × 4.2 mm ischemic lesion (white arrows) at the meso-diencephalic junction. COR = coronal, AX = axial, R = right. D The lesion (red) abutted the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF, blue) but not the interstitial nucleus of Cajal (INC, green). E Coronal reconstructions of the lesion (red), co-registered with a high-resolution (400 µm) MR-histology atlas (Juelich BigBrain, right half of image) and juxtaposed with matching histomorphological sections stained for myelin (Weigert, sudan black stain) and nuclei (kresyl violet, “Nissl”, both left side of image) reproduced with permission from (Mai JK, Majtanik M, Paxinos G. Atlas of the Human Brain. Academic Press; 2015). The lesion abuts the posterior commissure (PC) as well as an adjacent, Nissl-intense area of the dorsal midbrain, but not the interstitial nucleus of Cajal (INC) or the medial longitudinal fasciculus (MLF). Arrows also point to the aqueduct (AQ) for orientation