Examples of medial longitudinal fasciculus (MLF) lesions and recordings with infrared oculography. MLF lesions (arrow) on MRI with corresponding recordings of the patient of a rightward (left graph) and a leftward (right graph) saccade measured with infrared oculography. The X‐axis represent the time in milliseconds (ms), the Y‐axis the horizontal eye position in degrees (deg) of visual angle. The blue line represents the right eye, the red line represents the left eye. VDI values mentioned below represent mean VDI area under the curve (AUC) values of 15° saccades. (a) A clearly visible bilateral MLF lesion was found in the brainstem. This patient showed an evident bilateral INO, with a VDI AUC of 1.90 for rightward saccades and 1.53 for leftward saccades. (b) A large lesion was found in the right pons, with MLF involvement. This patient showed a leftward INO, with a VDI AUC of 1.10 for rightward saccades and 1.25 for leftward saccades. (c) A bilateral lesion was found in the lower pons to upper medulla oblongata, with MLF involvement. Based on the detection criteria, a mild bilateral INO was found. The leftward INO is not clearly visible on visual inspection of the recordings (right graph) and was only just above the threshold of detection with the VDI PvAm, not with the VDI AUC. The VDI AUC was 1.26 for rightward saccades and 1.12 for leftward saccades. (d) A clear right sided MLF lesion was found in the mid pons. This patient had a leftward INO, with a VDI AUC of 0.93 for rightward saccades and 1.32 for leftward saccades. (e) A bilateral MLF lesion was found in the lower pons. This patient demonstrated only a leftward INO, with a VDI AUC of 1.14 for rightward saccades and 1.20 for leftward saccades. (f) A lesion in the lower pons rated as left sided MLF lesion was found. In this patient there was no INO with infrared oculography measurement (VDI AUC of 1.05 for rightward saccades and 1.06 for leftward saccades). In retrospect, the lateral location of the lesion may just bypass the MLF. [Colour figure can be viewed at wileyonlinelibrary.com]