In addition to upper & lower eyelids, all woodpeckers have a third eyelid, called the nictitating membrane. It is translucent (they can see through it). The left photo shows nictitating membrane partially closed. Center photo shows the membrane covering the entire eye. Right photo shows the upper eyelid partially closed.
Nictitating membrane moves across the eyeball, from front to back, to clean it and protect the eye lens from flying debris when chiseling & hammering. Upper right is an animation of this action, hugely slowed down. I have only seen the nictitating membrane deployed in my photos, never in the field.