Why the white dot became a black dot in the optic nerve?

The white dot in the optic nerve likely represents an area of demyelination, where the protective myelin sheath around nerve fibers has been damaged or lost. This can occur due to various conditions, such as multiple sclerosis or optic neuritis, leading to a change in the appearance of the optic nerve. As the nerve fibers become more exposed, they may appear darker in color on imaging studies. This change signifies underlying pathology affecting optic nerve function.