You might say that someone with a keen sense of sight is "eagle eyed," but, unfortunately, that's wishful thinking. A bald eagle, gliding high above a meadow, searching for the telltale rustle of a passing mouse, has eyesight that is eight times more powerful than ours.
The eyes on an eagle's face may seem relatively small, but the part you can see is only the tip of the iceberg. The actual eyeballs, lying within an eagle's skull, are huge by our standards, taking up more room than the brain itself! Within these eyes, eagles have more light sensitive vision cells than we do.
While we have some two hundred thousand vision cells at the most concentrated part of our eye, eagles have one point five million. Their eyes are more sensitive to movement than they are to color. This sensitivity helps a soaring bird find its prey up to a mile away.
One drawback is that the eyes of a bird are fixed immovably in its skull. In order to change its point of view, a bird has to move its whole head. What's more, scientists estimate that up to eighty percent of an eagle's sensory input comes from its eyes. This leaves little left over for a sense of touch or taste or smell.
In fact, if you cover an eagle's eyes with a hood, the eagle will instantly go unconscious, its brain shutting down due to sensory deprivation. Because of this, it's possible for a doctor to perform minor surgery on an eagle without any anesthetic, only a hood over the eagle's eyes!