After taking a thorough history, the doctor will perform a careful examination that includes measuring the visual acuity, color vision, and peripheral visual field. In most cases of ischemic optic neuropathy, the doctor will see swelling of the optic nerve in the back of the eye. Depending on other clinical factors, some blood work may be done to exclude other diseases that affect the optic nerve. For example, it is important to exclude the possibility of Temporal Arteritis , which requires urgent treatment to prevent loss of vision in the other eye. Imaging studies (such as a CT or MRI scan ) are not usually needed to diagnose NAION, but might be performed in an atypical case.