a
really really really realy bad fungus...or frostbite
Starch.
Rusting
Mold
because it is li8mp and lifeless..
Gravitation.
Brake dust!
Bugs are wiping their asses on them
Poor circulation. You should see a doctor immediately!
It depends on how old you are and what your life expectancy is. Human eyes will not turn black during a person's life.
black because they get dirty and holes because they get worn out
Alkaptonuria is an inherited condition that causes urine to turn black when exposed to air.
Too much iron in the water