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a paralysis of one or more cranial nerves by which the eye muscles are innervated. Ophthalmoplegia may be congenital—a result of underdevelopment of the nuclei of the oculomotor nerves—or acquired as a sequela of inflammatory, toxic, or traumatic lesions in the brain. It can occur in one or both eyes.
Several forms of ophthalmoplegia are distinguished. External ophthalmoplegia is a paralysis of the external ocular muscles with retention of function in the internal muscles. Internal ophthalmoplegia is a paralysis of the internal ocular muscles with retention of function in the external muscles. Total ophthalmoplegia is a paralysis of both internal and external muscle groups. With the external form, the eyeball becomes rigid, although the pupillary reaction to light is not affected. With the internal form, the movements of the eyeball remain normal, but the pupillary reaction disappears and accommodation and convergence are impaired. Ophthalmoplegia is treated by eliminating the underlying cause.