Editing Trochlear nerve (section)

====Central lesion====
Central damage is damage to the trochlear nucleus. It affects the ''contralateral'' eye. The nuclei of other cranial nerves generally affect ''ipsilateral'' structures (for example, the optic nerves - cranial nerves II - innervate both eyes).

The trochlear nucleus and its axons within the brainstem can be damaged by infarctions, [[hemorrhage]], [[arteriovenous malformation]]s, tumors and [[demyelination]]. Collateral damage to other structures will usually dominate the clinical picture.

The fourth nerve is one of the final common pathways for cortical systems that control eye movement in general.  Cortical control of eye movement ([[saccades]], smooth pursuit, [[Accommodation (eye)|accommodation]]) involves [[Conjugate gaze palsy|conjugate gaze]], not unilateral eye movement.