Internuclear ophthalmoplegia

Internuclear Ophthalmoplegia (INO)

Introduction

Internuclear Ophthalmoplegia (INO) is a neurological disorder affecting eye movement. It is characterized by a deficit in the conjugate lateral gaze primarily involving impaired adduction in the affected eye.

Pathophysiology

Anatomical representation of brainstem regions involved in INO.

INO occurs due to a lesion in the medial longitudinal fasciculus (MLF), an area in the brainstem that coordinates eye movements. The MLF connects the abducens nucleus of one side to the oculomotor nucleus on the opposite side.

Clinical Presentation

In INO, the affected eye shows impaired adduction when attempting to gaze contralaterally. For example:

• If the right eye is affected, adduction is limited when attempting to look left.
• The contralateral eye abducts with nystagmus.
• Patients may experience horizontal diplopia, seeing two images side-by-side.
• Interestingly, convergence is usually preserved in INO.

Causes

Common causes of INO include:

• Multiple sclerosis (most common in young adults)
• Stroke (more common in older patients)
• Trauma
• Infections
• Neurodegenerative diseases

Diagnosis

Diagnosis is primarily clinical, supported by:

• Patient history and symptom analysis
• Neurological examination
• Imaging studies like MRI to identify lesions

Treatment and Management

Treatment of INO involves:

• Addressing the underlying cause (e.g., immunotherapy for multiple sclerosis, stroke management)
• Symptomatic relief (e.g., using prism glasses for diplopia)
• Rehabilitation and physical therapy

Prognosis

The prognosis of INO varies depending on the underlying cause. It may resolve spontaneously or persist, requiring ongoing management.

Epidemiology

INO is more common in individuals with risk factors for stroke or multiple sclerosis, though it can occur in various demographic groups.

See Also

• Eye movement
• Multiple sclerosis
• Stroke

External Links

• American Academy of Ophthalmology - Internuclear Ophthalmoplegia
• National Institute of Neurological Disorders and Stroke - Internuclear Ophthalmoplegia

Internuclear ophthalmoplegia Resources
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