Raptors have an extra eyelid referred to as a nictitating membrane. This semi-transparent body part acts rather like goggles that we might wear to protect our visual receptors from wind and dust.
I watched this hearty red-tailed hawk atop Mt Lemmon, one of the highest peaks in Southern Arizona, as a storm brewed around us. When winds began to intensify, the eyelid came down to protect his / her eyes. As the turbulence subsided, the piercing eyes yet again became visible.