Afterwork: Border, cropped, contrast, sharpened.

Sight is an eagle's most important sense. Scientists believe that an eagle's vision is as much as six times sharper than a human's even though the eyes are approximately the same size. The relatively large eye to head size is not obvious because most of the eye socket is surrounded by the skull. In fact the eye consumes so much of the skull that there is little room left for the muscles that move the eye. The eagle can compensate for the lack of eye mobility by rotating its neck. The large number of cervical vertebrae in the neck enable it to sweep a 270 degree arc.

Even though an eagle's eyes are located on the side of the skull, they protrude outward and their position is far enough forward to provide an overlapping field of view. This allows a degree of binocular vision and its associated depth perception. The ability to accurately perceive distances is critical when diving for prey and snatching it with talons.

The cornea or outer surface of the eye is protected by a ring of bones called the sclerotic eye ring and by two eyelids. The outer eyelid is similar to a human's and is closed from the bottom when sleeping. The inner transparent eyelid is called a nictitating membrane. It protects and keeps the eye moist and clear by flicking across the eye sideways every three or four seconds. Eagle parents often pull the membranes over their eyes when feeding their young. This prevents the eye from being accidently injured by the chicks when they lunge for their food.

The extremely soft lens of the eye allows for rapid accommodation. This ability to quickly refocus between near and far assists in prey identification and self protection. In addition, the eyes are partially atonomous which allows some independent monocular vision to the sides.



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