“Depending on the species, an owl’s eyes can account for 1-5% of its weight. As most owls are active at night, their eyes must be very efficient at collecting and processing light. This starts with a large cornea (the transparent outer coating of the eye) and pupil (the opening at the center of the eye). The pupil’s size is controlled by the iris (the coloured membrane suspended between the cornea and lens). When the pupil is larger, more light passes through the lens and onto the large retina (light sensitive tissue on which the image is formed).
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 colour. Cells that do react to colour are called “cone” cells (shaped like a cone), and an Owl’s eye possesses few of these, so most Owls see in limited colour or in monochrome.
Since Owls have extraordinary night vision, it is often thought that they are blind in strong light. This is not true, because their pupils have a wide range of adjustment, allowing the right amount of light to strike the retina. Some species of Owls can actually see better than humans in bright light.
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.” -The Owl Pages
Barred Owl (Strix varia) in our backyard in Woodinville, WA. 7/8/14.
Photo and description by Jacob McGinnis
Photography page: https://www.facebook.com/BirdPhotographyByJlm?ref=hl