Hypoplasia of this structure can be diagnosed by noting a DD to DM ratio less than 0.35.
Hypoplasia of this structure can be diagnosed by noting a DD to DM ratio less than 0.35. Because it can cause inflammation of this structure in children under 6, ethambutol is avoided to treat TB in that age group.  A disease in which this structure becomes inflamed is caused by autoantibodies to aquaporin-4. An increase in intracranial pressure can be diagnosed by the swelling of the "head" of this nerve, which is also called its namesake "disk"; that swelling is called papilledema. The superior colliculus and lateral geniculate nucleus eventually receive input from this nerve, which decussates at a structure that can be compressed by large tumors in the pituitary gland, its namesake chiasm. A mitochondrial disease named for Leber affects this nerve, which receives axonal projections from retinal ganglion cells.  For 10 points, name this cranial nerve that carries visual signals from the eye.
Hypoplasia of this structure can be diagnosed by noting a DD to DM ratio less than 0.35.
optic nerve [or cranial nerve II or CN  II or CN2]