||Watch the first segment of the video up to "Stop! What would you expect with vertical gaze?" and select the best response below. The patient also has mild right-beating nystagmus which can be ignored for the purposes of this question. ; A.; The patient has pupillary findings consistent with bilateral 3rd nerve palsies, and bilateral superior rectus palsies would be expected. ; B.; The patient has pupillary findings consistent with neurosyphilis, and complete vertical ophthalmoplegia would be expected. ; C.; The patient has pupillary findings consistent with an acute stroke, and downgaze palsy would be expected. ; D.; The patient is likely to have impaired upgaze due to involvement of the posterior commissure. ; Answers; A.; Incorrect. The patient has light-near dissociation, which is not typically seen with 3rd nerve palsies unless aberrant regeneration has developed. In his case, pupils are not mydriatic, there's no ptosis, and adduction is normal as seen with convergence. ; B.; Incorrect. Neurosyphilis may cause light-near dissociation involving unilateral or bilateral pupils (Argyll-Robertson pupils) due to presumed involvement of the pretectal nuclei, with brisk constriction to a near target as in this video. However, complete vertical ophthalmoplegia is not a typical finding in neuro-syphilis. That being said, since neurosyphilis can cause a wide range of peripheral or central ocular motor abnormalities, it should not be excluded completely based on the presence of vertical ophthalmoplegia. ; C.; Incorrect. Impaired downgaze tends to occur in conditions like progressive supranuclear palsy or disorders involving the rostral interstitial medial longitudinal fasciculus (riMLF, unilateral or bilateral strokes), but these conditions are typically unrelated to pupillary dysfunction. If a stroke was responsible for light-near dissociation (around the pretectal nuclei), a pure upgaze palsy (adjacent posterior commissure, although possibly related to unilateral 3rd nucleus ischemia) would be much more likely than a pure downgaze palsy (riMLF). ; D.; Correct. This patient has a dorsal midbrain (Parinaud's) syndrome due to a chronic neurosarcoidosis lesion. There is pupillary light-near dissociation related to involvement of the pretectum. The pupillary light reflex pathway begins in the retina/optic nerve, traverses the optic chiasm to optic tract, then travels via the brachium of the superior colliculus to the pretectal nuclei. Since all other axons synapse at the lateral geniculate nucleus, a lesion involving the brachium of the superior colliculus may cause an afferent pupillary defect without loss of field, acuity or color vision, as these fibers are spared. A dorsal midbrain lesion (usually compressive) will damage those fibers responsible for the pupillary light reaction that enter the Edinger-Westphal nucleus (EWN) caudally, while sparing those (accommodative) fibers responsible for the near response that enter the EWN more rostrally. With Parinaud's and Argyll-Robertson pupils, the constriction is brisk when looking at a near target, as opposed to the slow constriction seen with "tonic" pupils. Tonic pupils are thought to relate to ciliary ganglia injury, and may be associated with autonomic symptoms and signs and hypo or absent deep tendon reflexes, but should not be related to vertical eye movement abnormalities. The posterior commissure, which plays a role mainly in upgaze, will similarly be affected in this region. Upgaze paresis and convergence-retraction nystagmus (asynchronous convergent saccades with retraction of the globes) are commonly seen. Other commonly associated features with a Parinaud's syndrome include eyelid retraction, skew deviation, pseudoabducens palsy, and fixation instability (square-wave jerks). ; ; Summary; The patient was referred for oscillopsia related to new right-beating nystagmus that was unidirectional, but without left unilateral vestibular loss, making a peripheral vestibular localization very unlikely. MRI did not demonstrate new posterior fossa lesions or enhancement of the 8th cranial nerve on the left. Work-up for central causes is ongoing. The patient had a chronic neurosarcoidosis lesion involving the dorsal midbrain, which was responsible for his light-near dissociation, upgaze palsy and convergence-retraction nystagmus.