Ischemic damage to the optic nerve or ischemic optic neuropathy (ION) is a known complication of CABG. ION describes a defect of the optic nerve leading to irreversible loss of vision in most cases. Influenced by a variety of factors, pathophysiological microvascular changes are believed to provoke anterior ischemic neuropathy with sudden painless loss of vision. Since therapeutic trials have failed, there is no reliable and effective treatment of anterior ischemic optic neuropathy and prevention of possible causes is the only way to avoid this rare but severe complication of cardiac surgery. The following risk factors were determined for ION following CABG: History of glaucoma or other ophthalmological problems, prolonged cardiopulmonary bypass-time, myocardial ischemia, general edema during cardiopulmonary bypass, excessive hemodilution with low hemoglobin and hematocrit, hypo- or hypertension, systemic hypothermia, need for vasoactive medication, diabetes and anemia.