What do Raptors Use for "Goggles"?

What a wonderful sight to see a bald eagle soaring!  In the first photo of our post today, though, do you notice anything different?

In this close-up you can see that there is something covering the eyes!  It is called a nictitating membrane. 

A nictitating membrane acts much like a pair of “goggles” for raptors.  In flight, raptors can see through this third eyelid, and it will keep the eye safe from dust and other objects in the air.  It also keeps the eye moist.

This is the same bird, in a subsequent frame.

You can see that the eye is uncovered for a moment in the bird's flight, and that there is nothing wrong with the eyes.