Diagram of normal eye movement compared to left one-and-a-half syndrome (i.e. left lateral gaze palsy, with left Internuclear ophthalmoplegia (inability to adduct))
Causes
Demyelinating disease, e.g. Multiple sclerosis
Infarction
Infections, e.g. Brainstem encephalitis and Neurocysticercosis
Tumours
Arteriovenous malformation
Pontine haemorrhage
Basilar artery aneurysms
Trauma
Differential diagnosis
Neuromyelitis optica spectrum disorder
Myasthenia Gravis
The one and a half syndrome is a rare weakness in eye movement affecting both eyes, in which one cannot move laterally at all, and the other can move only in outward direction. More formally, it is characterized by "a conjugate horizontal gaze palsy in one direction and an internuclear ophthalmoplegia in the other".[1][2] Nystagmus is also present when the eye on the opposite side of the lesion is abducted. Convergence is classically spared as cranial nerve III (oculomotor nerve) and its nucleus is spared bilaterally.
^Wall M, Wray S (1983). "The one-and-a-half syndrome--a unilateral disorder of the pontine tegmentum: a study of 20 cases and review of the literature". Neurology. 33 (8): 971–80. doi:10.1212/wnl.33.8.971. PMID 6683820. S2CID 35636994.
^Siegel A, Sapru HN (2006). Essential Neuroscience (1st ed.). Baltimore, Maryland: Lippincott, Williams, & Wilkins. pp. 190–191. ISBN 978-0-7817-9121-2.
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