> The retina is one of the body’s most energetically expensive tissues.
I never knew, but it explains why when you close to fainting you lose your vision. Or when you are working at high heart rate close to your maximum. It works as a kind of a warning sign, than you are probably shouldn't try it that hard.
> The lack of blood vessels could also offer birds the advantage of better vision.
Now they are ready to reintroduce blood vessels back, but this time behind the retina.
How does it explain either of those things?
When you have not enough oxygen it breaks. And parts using a lot of it fail first. Vision fails first, not memory, or thinking. Thinking is impaired but still works.
I'm not sure how fainting works, but fainting looks to me like an energy crisis, so kinda not surprising the results are the same.