For some reason mankind is fascinated with birds. There are countless expressions based on birds. Phrases such as "this is for the birds" or even "swift as a bird" are quite common. Perhaps it is the sight of wild birds soaring through the skies that gives mankind the feeling that they have the best of it all. Even the term "bird's eye" is used so commonly that most people know what someone is referring to. But literally, the bird eye is something to envy.
The bird eye and the human eye share many of the same structures. Both eyes have many of the same functions as well. A few of the basic structures of a bird's eye, no matter the species of birds, are cornea, retina, anterior chamber, iris, lens, and eyelids. Humans have these same structures but the difference is how the structures work. Take for example the size of the eye. A human eye is only 1% of their body. A starling's eye is 15% of its body. Birds can see a great deal better than humans but we do have the advantage of being able to move our eyes.
The size of the eye depends on the bird species. Owls, for example, have huge eyes that allow them to take in more at once. For a wild bird that is important because it means that they can spot enemies and their prey much easier. Owls cannot move their eyes so they rotate their heads. How far do they rotate their heads? They rotate a whopping 200 degrees. Another difference to be found is the number of eyelids a bird has over humans. The human eye only has an upper and lower eyelid.
All species of birds have three eyelids. They have an upper, lower and a nictitating membrane that cleans and protects the eye. Another difference is in the positioning of the eyes. Humans and most wild animals, especially predators, have eyes that are not as centralized as a bird's eye. A bird's eye is on the front of the skull and they lack the ability to see very far to the sides. This is why birds turn their heads often.
The bird eye is a complex and fascinating organ. And while it may share many of the same structures and functions as a human eye, it is somewhat superior. Wild birds depend on their eyesight. If something were to happen to its eyes or even just to one of the eyes, it would have drastic and dire consequences, in terms of survival.
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