Unless you were born blind you already know how valuable your eyes and vision are in coping with life. Helping us to process information on the world around us, our eyes constantly work to help us enjoy life and avoid danger.
Dogs also use their eyes in similar ways but with a few minor important differences. We see far and near fine detail in a wide range of colors and shades. Dogs however, even sight hounds which have good vision, have a poorer color range and they are much better at detecting movement rather than detail. This gives them an advantage with night vision but they are poorer at seeing fine or close detail. The main advantage dogs have is that they don't have to rely purely on vision for information on their world. An acute sense of smell and excellent hearing, along with good motion sensing vision, mean that dogs sense much more of their surrounds than mere humans. This extended sensory ability made them ideal companions to early man when danger lurked around every corner.
Dogs eyes even look remarkably similar to human eyes. Like us, dogs have a range of eye colors although their predominant color is brown. One important difference between us is that dogs have a third eyelid called a nictitating membrane. Although this membrane is not easily seen, certain diseases and eye irritation can make it stand out. The third eyelid sits in the inside corner of a dogs eye and helps to protect it from irritation by cleansing and lubricating the eye.
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Most of the eye diseases and problems seen in dogs are the same as those found in humans. One of the most common problems seen in dogs is due to simple eye irritation. The same environmental irritants that afflict us afflict our dogs. Dust, smoke and chemical pollution are the commonest cause of watery irritable eyes in our favorite pets. Apart from seeing red, teary eyes which are often swollen, you will likely observe your dog rubbing or scratching at their eyes. Look carefully at whether both or only one eye is irritated. Symptoms occurring in only one eye usually mean a foreign body or injury in the eye involved.
Blocked tear ducts can also produce excessively watery eyes in dogs as well as humans. In some dog breeds, such as older Poodles and Shih Tzu's, you will often see damp matted fur around their eyes that signals tear duct blockages. An expert opinion from a vet is often needed to tell the difference between the different causes of watery eyes.
Another trait that elderly dogs share with elderly humans is the development of cataracts. Most long term dog owners have seen the cloudy milky haze that spreads in the centre of each pupil as the cataracts form. This milky haze is the lens inside your dogs eye becoming opaque and the dog slowly becomes blind. It's important to distinguish cataract from another change called Lenticular Sclerosis. Lenticular Sclerosis is a condition which looks similar to cataract but where the only the center of the dogs lens hardens and vision remains unaffected. Both problems are seen in elderly dogs.
One significant advantage that aging dogs have compared to humans is that eye damage and blindness does not incapacitate them to the same extent as human blindness. Good hearing and an acute sense of smell compensate well. There are many stories told of blind dogs managing wonderfully well in life and it's a pity we aging humans are unable to see through the "eyes" of our beloved dogs at times!