Vasculopathic: Observation for improvement over 6-8 weeks. Often resolve spontaneously in 4-6 months.
Traumatic:  Observation for improvement over 6-8 weeks. Often resolves spontaneously. If progressing or lack of improvement – neuroimaging with MRI
Isolated, idiopathic cases very rarely have an underlying etiology after prolonged follow-up, and most resolve spontaneously in weeks to months. If no improvement in 2 months, consider neuroimaging.
Fourth nerve palsy
Increased intracranial pressure 
Third nerve palsy
Vascular:  Stroke, subarachnoid hemorrhage, aneurysm 
Sixth nerve palsy
Neoplastic: Tumor in the subarachnoid space
Ulnar neuropathy
Degenerative/deficiency: Vitamin B12 deficiency, Wernicke-Korsakoff syndrome