Dog eye (Photo credit, deviantart)
Dog Eyes
Now we are going to look at canine eyes. The socket in which the eye resides is called the orbit, the orbit is a structure that is formed by several bones. It also contains muscles, nerves, blood vessels, and tear ducts. The white of the eye is called the sclera, and is a relatively tough layer covered by a thin membrane. This membrane also covers the cornea, which is the clear dome in the front center of the eye that lets light in. And that brings us to the iris. The iris is the circular, colored area of the eye, it controls the amount of light that enters the eye by making the pupil larger or smaller. When the environment is dark, the pupil enlarges to let in more light; when the environment is bright, the pupil becomes smaller to let in less light. The lens, which sits behind the iris, changes its shape to focus light onto the retina. Small muscles (ciliary muscles) contract to cause the lens to become thicker, which allows the lens to focus on nearby objects. They can also relax to cause the lens to become thinner when it focuses on distant objects. The retina contains the cells that sense light (photoreceptors). These lens changes are limited in dogs. The most sensitive area of the retina is called the area centralis. This area contains thousands of tightly packed photoreceptors that make visual images sharp. Each photoreceptor is attached to a nerve fiber. And all the nerve fibers are bundled together to form the optic nerve. The photoreceptors in the retina convert the image into electrical impulses, which are carried to the brain by the optic nerve. The upper and lower eyelids are thin folds of skin that can cover the eye and reflexively blink to protect the eye.Blinking also helps spread tears over the surface of the eye, keeping it moist and clearing away small particles. The eyes of a dog are protected not only by the same types of eyelids that people have, but also by the nictitating membrane, which is sometimes called the third eyelid. This additional eyelid is a whitish pink color, and is found under the outer eyelids in the inside corner of the eye (near the nose). The third eyelid extends across the eye when needed to protect the eyeball from scratches (for example, while traveling through brush) or in response to inflammation. Most animal’s eyes seem so similar, yet if you really take a look you can see that they’re more than meets the eye. (Sorry I had to)
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