The role of ascorbate in the vitreous cavity. A, The vitreous acts as a barrier to the diffusion of oxygen within the posterior segment. The available ascorbate binds with oxygen, forming dehydroascorbate, which is taken up by surrounding cells. B, In postvitrectomized eyes, the amount of oxygen exceeds the capacity for clearance, leading to the production of reactive compounds that create oxidative stress in the lens, which in turn accelerates cataract formation.