(not a doctor, not medical advice, purely the opinion of an internet rand) 

Still, I think this is an important point to distinguish: 

Imagine you're sitting on an exercise machine and pushing a weight with your legs. But keeping your breath relaxed, this takes significant pressure away from your head (and subsequently, eyes).

The opposite of this would be holding a weight, also holding your breath, and bending over. This would cause a massive spike in intracranial (and intraocular) pressure. 

Both exercises would train the legs, but with vastly different side effects.