How Dogs See
How do dogs see? The location of the dog's eyes are important to how the eyes work. Dog's eyes are located in the front of the face, mainly becasue they are predators and frontal positon allows for focus and accuracy in distance judgment. Further, a dog's vision is described as binocular vision, meaning the eyes working together in frontal position.
Well let's cut it right down to each part of the dog's eye and how it works.
Anatomy of the Dog's Eye
Optic Nerve - The optic nerve carries the electrical impulses from the eye to the area in the back of the brain.
Optic Disk - The centre of the retina has more of the light- sensitive cells known as rods, which work better in dim light than the colour-detecting cones. The light sensitive compounds in the retina respond to lower light levels. The lens is positioned closer to the retina, making the image on the retina brighter.
Vitreous body - It is about 99% water, but usually is present in a gel state due to its collagen content. Besides being optically clear to allow light to reaxh the retina, the viteous body is important for the metabolism of intraocular tissues.
Lens - The lens of the eye is the clear structure within the eye which focuses the light onto the retina where vision occurs. The lens is located behind the iris, the central portion being exposed by the pupillary opening.
Ciliary body - The ciliary body, which is the tissue immediately behind the iris lying between the iris and the choroid; the iris and ciliary body make up the anterior uvea and the choroid is called the posterior .
Iris - The iris can be one of several different colours and some dogs have 2 different colour irises. Some, but not all dog with blue eyes are deaf. Dalmatians are one breed that can suffer with deafness when it comes to having blue eyes. The job of the iris is to control the amount of light that enters the eys. It dose this by adjusting the size of the opening in its centre, the little black dot known as the pupil. And it's the iris that gives your dog's eyes their colour.
Anterior Chamber - The anterior chamber (AC) is the fluid-filled space inside the eye between the iris and the cornea's innermost surface, the endothelium. One peculiar feature of the anterior chamber is impeded immune response to allogeneic grafts.
Cornea - The cornea is the transparent, shiny membrane which makes up the front of the eyeball. Think of it as a clear window. The cornea is comprised of three layers. The most superficial layer is the epithelium. This layer is comprised of several very thin layers of cells. Below the epithelium is the stroma, and the deepest layer is Descemet's membrane.
The way a dog's eyes work to produce vision, is when the light enters the eye and is absorbed by sensory cells. These sensory cells have two types of receptors called rods and cones; these are located in the retina which transmits signals to the dog's brain, where an image appears. The retina is considered a part of the dog's brain but it is actually located in the outside of the brain. The retina is a thin film of nerve tissue at the back of the dog's eye and is very sensitive to light.
The sharpest vision is where cells are most dense. The dog has two areas where sensory cells are arranged densely. One area is the centralis, an Australian scientific researcher said the cells are arranged in circles. The Australian Veterinary Scientist Paul McGreevy established that dog's eye shape changed with different dog breeds.
Apparently his colleague Alison Harman discovered after examining the retinas of different breeds of dogs, not only was the eye shape different, but so was the retina. Some breed of dogs didn't possess any horizontal bands with rods, where other breeds do. This also explained why some dogs have a wider field of vision than other dogs. So this means some dogs may see the world completely differently to others.
Peripheral vision is simply side vision; it's the vision outside the centre of the frontal gazing. Dog's peripheral vision is better than humans. Dogs with a long nose are better hunters for this reason; their eyes work to recongnize prey at long distances. A dog that runs an agility course uses peripheral vision at its finest.
We humans see objects more clearly; in dogs their other senses are more powerful than their eyes. A dog's vision is less sharp then ours, but in the dark their sight is better than ours. Now if you stand quietly at the end of a field, your dog will not see you until you start moving. Dogs find it much easier to see moving objects.
Now what about dog's night vision. A dog's vision in the dark is far superior to ours. The lens and cornea can take in more light in the darker surroundings. The lens and cornea work together to refract light.
Have you ever let your dog out in the garden at night and been trying hard to call him in, hen ended up going out in your PJ's to get him in, and wondered why your dog stands still and looks at you, with those yellowish glowing eyes (like something from the 'Hound of the Baskerviles)? Well even though he can see well in the dark, he still not sure who is there, so moving about and talking to him will reassure him its you. Which is a very good idea becuase you wouldn't want him to turn to the hound would you!
A question that has been asked so many time is, do dogs see colour? The answer is yes, but not in the way we do. Dogs don't see all the colours we do. Dogs see colour like people who suffer with colour blindness. Dogs can't tell the difference between yellow, orange, red and green.
I have seen many people throw a green tennis ball for their dog to find on grass. The dog is not finding the ball by sight as he can't see the green ball in the grass. They find it by smell. I have often smiled to myself and thought, if a dog could talk, he would tell us to go and get the ball our self as we can find it in the grass!
I hope by reading this subject about how dogs see, you will have a better understanding about your dog and how he sees in our world. The most important thing to remember is no matter how your dog sees you; his love for you is unconditional.
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