One and a half syndrome
The one and a half syndrome is a rare ophthalmoparetic syndrome characterized by "a conjugate horizontal gaze palsy in one direction and an internuclear ophthalmoplegia in the other". The most common manifestation of this unusual syndrome is limitation of horizontal eye movement to abduction (moving away from the midline) of one eye (e.g. right eye in the diagram on the right) with no horizontal movement of the other eye (e.g. left eye in the diagram on the right). 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.
The syndrome usually results from single unilateral lesion of the paramedian pontine reticular formation and the ipsilateral medial longitudinal fasciculus. An alternative anatomical cause is a lesion of the abducens nucleus (VI) on one side(resulting in a failure of abduction of the ipsilateral eye and adduction of the contralateral eye = conjugate gaze palsy towards affected side), with interruption of the ipsilateral medial longitudinal fasciculus after it has crossed the midline from its site of origin in the contralateral abducens (VI) nucleus (resulting in a failure of adduction of the ipsilateral eye).
- 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. PMID 6683820.
- Siegel A, Sapru HN (2006). Essential Neuroscience (1st ed.). Baltimore, Maryland: Lippincott, Williams, & Wilkins. pp. 190–191. ISBN 978-0-7817-9121-2
- Kipioti A, Taylor R (2003). "Botulinum toxin treatment of "one and a half syndrome"". Br J Ophthalmol 87 (7): 918–9. doi:10.1136/bjo.87.7.918-a. PMC 1771745. PMID 12812899.
- 1060438082 at GPnotebook - This link incorrectly states that the contralateral eye can still adduct. It can only abduct with nystagmus.
- Video at University of Utah