The lid and the skull hide most of it. If humans had the same eye to head proportions that owls have, our eyes would be as big as grapefruits. But what the owl can do, thanks to specialized neck bones and muscles, is move its head rapidly, far to either side, increasing its field of vision to 270 degrees. In the retina at the back of the eye, are cones and rods, tiny light-sensitive cells that act as receptors and form images. Cones distinguish colors, function in bright light, and are needed for sharp vision.
Rods function in low light or at night.
As would be expected with birds that hunt mainly at night, an owl's eyes contain a lot of rods. In fact, an owl's ability to see sharply is as developed as in any kind of bird, including hawks. Rods contain a pigment called visual purple, which is what enables an owl's eyes to adapt to the dark. Owls can control the pupil of each eye separately, responding to different light intensities from different parts of its environment. Another attribute that may help account for an owl's extraordinary eyesight is the shape of its eye.