Ocular Motor Dysfunction Due to Brainstem Disorders

The brainstem contains numerous structures including afferent and efferent fibers that are involved in generation and control of eye movements. These structures give rise to distinct patterns of abnormal eye movements when damaged. Defining these ocular motor abnormalities allows a topographic diagnosis of a lesion within the brainstem. Although diverse patterns of impaired eye movements may be observed in lesions of the brainstem, medullary lesions primarily cause various patterns of nystagmus and impaired vestibular eye movements without obvious ophthalmoplegia. By contrast, pontine ophthalmoplegia is characterized by abnormal eye movements in the horizontal plane, while midbrain lesions typically show vertical ophthalmoplegia in addition to pupillary and eyelid abnormalities. Recognition of the patterns and characteristics of abnormal eye movements observed in brainstem lesions is important in understanding the roles of each neural structure and circuit in ocular motor control as well as in localizing the offending lesion.