Eagles basically have little heads and big eyes; their eyes are large compared to their heads. What this means for an eagle’s eyesight is that he can see more because his field of vision is large. Eagles can soar and survey the landscape for potential food sources. Eagles also have an advantage over people in that people see three basic colors whereas eagles see five. Eagle eyes have many sensory cells. PBS notes that humans have 200,000 light-sensitive cells per square millimeter of retina, while eagles leave humans in the dust with about 1 million light-sensitive cells per square millimeter of retina.
Eagles can see to the front and to the side, thanks to foveae; Oxford Dictionaries defines the singular form of the word, fovea, as “a small depression in the retina of the eye where visual acuity is highest.” Humans only have one fovea and so only see forward with some peripheral vision. Eagles have more than a little peripheral vision. They can look at objects sideways as well as they can forward. Their forward and side vision overlaps. Eagles cannot roll their eyes like people can though. Eagles cannot move their eyes much at all, but they have a way around that. They can rotate their heads in nearly a full circle. A circle is 360 degrees, and eagles can twist their heads to about 270 degrees.
Some eagles, such as the bald eagle, change their eye colors through their lifetimes. Baby bald eagles have brown eyes, and later, when the eagles are adults, their eyes are yellow. Bald eagles also have two eyelids, which serve several purposes. One is to protect baby eagles’ eyes while they are feeding. The inner eyelid is see-through and also helps keep eagle eyes wet and free of debris. When bald eagles sleep, they close their eyelids, like humans do. While people are not supposed to look directly at the sun, bald eagles can, thanks to their second eyelids and their eyebrows. (source Ehow.com)