MSH: Atrophy of the optic disk which may be congenital or acquired. This condition indicates a deficiency in the number of nerve fibers which arise in the RETINA and converge to form the OPTIC DISK; OPTIC NERVE; OPTIC CHIASM; and optic tracts. GLAUCOMA; ISCHEMIA; inflammation, a chronic elevation of intracranial pressure, toxins, optic nerve compression, and inherited conditions (see OPTIC ATROPHIES, HEREDITARY) are relatively common causes of this condition.,NCI: A disorder characterized by loss of optic nerve fibers. It may be inherited or acquired. Acquired causes include ischemia, optic nerve neuropathy, glaucoma, trauma, radiation, brain tumors, and multiple sclerosis. It leads to vision disturbances.