[Aerroon]

My understanding is that glucose diffuses from the pecten oculi into the vitreous humor (it's the jelly-like thing that makes up most of the eyeball) and from there glucose diffuses into the inner retina.

I'm not sure why this is easier, but I'm guessing it has to do with how much oxygen you need for aerobic glycolysis. In blood, glucose just exists in the plasma by itself, oxygen has to be carried by red blood cells. Without blood vessels it's probably difficult to get enough oxygen through diffusion into the inner retina.

Fun fact: the human cornea also doesn't have blood vessels. Instead oxygen diffuses from the atmosphere into it and from the aqueous humor - a fluid? behind the cornea. The aqueous humor is also where the cornea (and the lens) get nutrients from.

Yep, your cornea basically breathes!