A: In normoxia, RGCs are metabolically supported (blue arrows) by astrocytes and oligodendrocytes, the latter only present in the myelinated portion of the optic nerve. B: In hypoxia, there is increased CHOP and GFAP co-expression in the unmyelinated portion of the optic nerve, which is consistent with ER stress and reactivity in astrocytes. Combined with loss of oligodendrocytes (C), this hypoxic condition creates optic nerve stress, impairing normal homeostasis and metabolic support (red arrows) in the retina and optic nerve. PO2: partial pressure of oxygen.