Internuclear ophthalmoplegia (INO) is a disorder of conjugate lateral gaze in which the affected eye shows impairment of

adduction Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...

. When an attempt is made to gaze contralaterally (relative to the affected eye), the affected eye adducts minimally, if at all. The contralateral eye abducts, however with

nystagmus Nystagmus is a condition of involuntary (or voluntary, in some cases) eye movement. Infants can be born with it but more commonly acquire it in infancy or later in life. In many cases it may result in reduced or limited vision. Due to the invol ...

. Additionally, the divergence of the eyes leads to horizontal

diplopia Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often v ...

. That is if the right eye is affected the patient will "see double" when looking to the left, seeing two images side-by-side.

Convergence Convergence may refer to: Arts and media Literature *''Convergence'' (book series), edited by Ruth Nanda Anshen *Convergence (comics), "Convergence" (comics), two separate story lines published by DC Comics: **A four-part crossover storyline that ...

is generally preserved.

Causes

The disorder is caused by injury or dysfunction in the

medial longitudinal fasciculus The medial longitudinal fasciculus (MLF) is an area of crossed over tracts, on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem. They are made up of both ascending and descending fibers that ari ...

(MLF), a heavily myelinated tract that allows conjugate eye movement by connecting the

paramedian pontine reticular formation The paramedian pontine reticular formation, also known as PPRF or paraabducens nucleus, is part of the pontine reticular formation, a brain region without clearly defined borders in the center of the pons. It is involved in the coordination of eye ...

(PPRF)-

abducens nucleus The abducens nucleus is the originating nucleus from which the abducens nerve (VI) emerges—a cranial nerve nucleus. This nucleus is located beneath the fourth ventricle in the Anatomical terms of location, caudal portion of the pons, Anatomical t ...

complex of the contralateral side to the

oculomotor nucleus The fibers of the oculomotor nerve arise from a nucleus in the midbrain, which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. From t ...

of the ipsilateral side. In young patients with bilateral INO,

multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...

is often the cause. In older patients with one-sided lesions a stroke is a distinct possibility. Other causes are possible.

Variants

A rostral lesion within the midbrain may affect the convergence center thus causing bilateral divergence of the eyes which is known as the WEBINO syndrome (Wall Eyed Bilateral INO) as each eye looks at the opposite "wall". If the lesion affects the PPRF (or the abducens nucleus) and the MLF on the same side (the MLF having crossed from the opposite side), then the "

one and a half syndrome 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 ...

" occurs, with paralysis of all conjugate horizontal eye movements other than abduction of the eye on the opposite side to the lesion.

Diagnosis

Can be seen in multiple sclerosis, stroke, and other pathologies. Accompanying symptoms include scanning speech,

intention tremor Intention tremor is a dyskinetic disorder characterized by a broad, coarse, and low frequency (below 5 Hz) tremor evident during deliberate and visually-guided movement (hence the name intention tremor). An intention tremor is usually perpendi ...

, incontinence, and nystagmus.

References

External links

{{Lesions of spinal cord and brain Disorders of ocular muscles, binocular movement, accommodation and refraction

Causes

Variants

Diagnosis

See also

References

External links