Of all an owl’s features, perhaps the most striking is its eyes. The forward facing aspect of the eyes that give an owl its “wise” appearance, also give it a wide range of “binocular” vision (seeing an object with both eyes at the same time). This means the owl can see objects in 3 dimensions (height, width, and depth), and can judge distances in a similar way to humans.
An owl’s eyes are large in order to improve their efficiency, especially under low light conditions. In fact, the eyes are so well developed, that they are not eye balls as such, but elongated tubes. An owl cannot “roll” or move its eyes – that is, it can only look straight ahead. The owl makes up for this by being able to turn its head up to 270 degrees left or right and almost upside down.
The retina of an owl’s eye has an abundance of light-sensitive, rod-shaped cells appropriately called “rod” cells. Although these cells are very sensitive to light and movement, they do not react well to color. Owls have extraordinary night vision, but see in limited color.
To protect their eyes, owls are equipped with 3 eyelids. They have a normal upper and lower eyelid, the upper closing when the owl blinks, and the lower closing up when the owl is asleep. The third eyelid is called a nictitating membrane, and is a thin layer of tissue that closes diagonally across the eye, from the inside to the outside. This cleans and protects the surface of the eye.
For protection from predators some insects have well developed eye spots. Owl Butterflies are large, tropical butterflies found in secondary forests and rain forests from Mexico down to the Amazon in South America. It is easy to see why they are called Owl Butterflies. Their wings look like the face of an owl, and if you spread the wings out, you can actually see a pair of eyes looking straight at you. Of course they cannot blink.