||This article relies largely or entirely upon a single source. (May 2011)
Ischemic optic neuropathy (ION) is the loss of structure and function of a portion of the optic nerve due to obstruction of blood flow to the nerve (i.e. ischemia). ION is typically classified as either anterior ischemic optic neuropathy or posterior ischemic optic neuropathy according to the part of the optic nerve that is affected. People affected will often complain of a loss of visual acuity and a visual field, the latter of which is usually in the superior or inferior field. 
See also 
- ^ editor, Cynthia A. Bradford, executive (2004). Basic ophthalmology (8th ed. ed.). San Francisco: American Academy of Ophthalmology. pp. Chapter 2. ISBN 1560553618.
- Dictionary of Eye Terminology, Triad Publishing Company, 1990.