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. It's tubular, not spherical like ours. This tubular shape gives the owl good telescopic vision.
Owls have a balance between hearing and seeing.
The eyes are in the middle of a disk of feathers, which are highly specialized sound conductors. The owl can flex these facial disks, channeling sound waves to the ears to catch even the faintest of sounds. An owl's ears are elaborate structures. These flaps expand, contract, and adjust the ear opening size. Many owls have asymmetrically developed ears, that is, the right external ear canal may be a different shape than the left external ear canal and each could be located higher or lower than horizontal on the side of the head.