In particular, we were discussing the fact that owls have small feathers on their eyelids and the discussion got around to the additional fact that many birds also posses a nictitating membrane which serves as a "middle" eyelid that allows the bird to blink without having to move the larger outer eyelid. The nictitating membrane allows most birds to blink but lets them to retain their vision as the membrane is usually semi-transparent. This membrane also moves differently from the usual eyelid as it closes horizontally over the eye rather than vertically. Occasionally when photographing birds, you may capture this nictitating membrane in mid blink and it creates a most interesting view as you see here. In this image I think the eagle looks like it could be a character out of the X - Men comics and movies.
Tawny eagle with nictitating membrane in place.
Here's an image of the same Tawny Eagle moments later....
By the way, you do not posses a nictitating membrane, but the corner of your eye next to your nose does have the remnants of an vestigial nictitating membrane called the plica semilunaris. To see other interesting animal postings, visit Camera Critters!