Multiple sclerosis; optic nerves: The optic nerves, optic chiasm, and optic tracts (which contain central nervous system myelin) are commonly involved in multiple sclerosis. The optic nerves are in the bottom half of the slide and the optic chiasm (incomplete) is in the middle. Note the extreme pallor of the optic nerve on the right as compared with the left in this myelin stain. Visual field defects are a common feature of multiple sclerosis.