- Teresa C Frohman, PA-C
Teresa C Frohman, PA-C
- Associate Professor of Neurology
- Managing Director of the MS and Neuroimmunology Center
- University of Texas at Austin Dell Medical School
- Elliot M Frohman, MD, PhD
Elliot M Frohman, MD, PhD
- Professor of Neurology
- Director of the MS and Neuroimmunology Center
- University of Texas at Austin Dell Medical School
Internuclear ophthalmoparesis (INO), also commonly referred to as internuclear ophthalmoplegia, is a specific gaze abnormality characterized by impaired horizontal eye movements with weak adduction of the affected eye, and abduction nystagmus of the contralateral eye. It is one of the most localizing brainstem syndromes, resulting from a lesion in the medial longitudinal fasciculus (MLF) in the dorsomedial brainstem tegmentum of either the pons or the midbrain .
Foveation or visual targeting with binocular fusion and stereoscopy (depth perception) requires highly synchronous eye movements that place objects of visual interest on the corresponding points of both retinas. This process is dependent upon the precise coordination between cranial nerves III, IV, and VI, and their interneuronal pathways that project through the medial longitudinal fasciculus (MLF) (figure 1).
The paramedian pontine reticular formation (PPRF) is often referred to as the conjugate gaze center for horizontal eye movements. During horizontal eye movement, the PPRF burst cells innervate the abducens nucleus, which contains two distinctive sets of neurons:
●Axons of the abducens motor neurons directly innervate the ipsilateral lateral rectus muscle.
●Axons of the abducens interneurons cross the midline to become the MLF and subsequently innervate the medial rectus subnucleus of the oculomotor complex (cranial nerve nucleus III). Motor neurons from this subnucleus innervate the medial rectus muscle (ipsilateral to the medial rectus subnucleus and contralateral to the abducens nucleus).To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:
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- OCULOMOTOR CIRCUITRY
- CLINICAL FEATURES
- - Adduction weakness
- - Normal convergence
- - Abduction nystagmus
- - Abduction slowing
- - Abnormal vertical eye movements
- Associated syndromes
- - One-and-a-half syndrome
- - Wall-eyed bilateral INO
- - Eight-and-a-half syndrome
- Multiple sclerosis
- Cerebrovascular disease
- DIFFERENTIAL DIAGNOSIS
- EVALUATION AND DIAGNOSIS
- Magnetic resonance imaging
- PROGNOSIS AND TREATMENT
- SUMMARY AND RECOMMENDATIONS