Here's a nice photo of some owls that we bumped in to at Castle Espie on Sunday. Don the Owl Man was not at all precious with his birds and allowed us to handle them. There are some more photos here. Apparently the big boyo on the left in the photo, a European Eagle Owl was attacked by a goose when he was last at Castle Espie. Shows how tough a goose is, the Eagle Owl can take on and kill a buzzard would you believe.
Don had a few more birds with him, a barn owl and a tawny owl. The Tawny Owl has a second eye lid, perhaps the others do, I didn't notice. This is a tough membrane that closes over the eye just before a kill, this protects the owl from any scratches from it's prey.
Actually after a quick google.

Owls have three eyelids. One at the top and one at the bottom of each eye, like humans, and a third one that goes from the inside corner across the eye. The third eyelid is called the nictitating membrane. It is thinner than the other eyelids and can help to protect the owl’s eyes when it is diving into the grass or other plants to catch animals or birds hiding there.
http://www.hawkandowl.org/page104a.html