Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 96. Cranial Nerve Disorders

Topics: Introduction | Internuclear Ophthalmoplegia | Palsies of Cranial Nerves That Control Eye Movement | Trigeminal Neuralgia | Bell's Palsy | Hemifacial Spasm | Glossopharyngeal Neuralgia | Hypoglossal Nerve Disorders

Internuclear Ophthalmoplegia

Internuclear ophthalmoplegia is weakness or paralysis of eye movements caused by damage to the nerve fibers connecting collections of nerve cells (centers or nuclei) that give rise to cranial nerves III (oculomotor nerve) and VI (abducens nerve).

In internuclear ophthalmoplegia, nerve fibers necessary for the control of horizontal and vertical eye movements--looking from side to side and up and down--are damaged. The most common causes are stroke in older people and multiple sclerosis in younger people.

Horizontal eye movements are impaired, but vertical ones are not. The eye on the affected side cannot turn inward when looking to the opposite side but can turn outward. Nystagmus occurs in the eye on the opposite side when it turns outward; that is, the eye moves rapidly in one direction, then drifts more slowly back to the original position.

A stroke may also damage the center for horizontal eye movements, resulting in the one-and-a-half syndrome. The eye on the affected side remains fixed in the middle. The other eye can turn outward but not inward. As in internuclear ophthalmoplegia, vertical eye movements are not affected.

Treatment of internuclear ophthalmoplegia depends on the cause. Whether internuclear ophthalmoplegia eventually resolves depends on the disorder that caused it.