Dogs, cats and human eyes have many similarities in the way that they function and allow us to see, but at the same time a few differences. For example, the lens of the dog and the cat is much bigger than the human lens, making procedures such as cataract surgery more challenging in these species.
The way that we perceive the world and the colours surrounding us, is also quite different when comparing what a human and dogs can see.
What do dogs see?
When we think of dogs, many examples of different breeds will come to mind, all of them equally adorable! However, their size matters when it comes to what they can see.
If you think of the height of a small Jack Russell Terrier, the height of a medium sized Staffordshire Bull Terrier or the height of a Great Dane, it will instantly become clear that the position of their head and eyes vary quite a lot.
The illustration below gives an example of the different perspectives of a small dog (A), a medium sized dog (B) and a human (C).
How do dogs see?
Images of the surrounding environment, toys, food or people, must pass a series of structures of the eye before they reach the optic nerve, which is responsible for transferring the information to our brain where the information is translated to what we perceive as vision.
The first structure is located at the outermost part of the eye (at the surface of the eye) is called the cornea.
The cornea is the clear part of our eye which allows the light to travel through the fluid located in the eye (called the aqueous humour) and meet the second most important structure, the lens.
The lens is surrounded by the iris (the coloured part of our eye) and through the pupil (the opening located at the centre of the iris), allows transmission of the light to further structures at the back of the eye.
At the back of the eye, the light is absorbed and processed by the retina and this information is sent to the optic nerve which will then relay to the brain.
In this simplified example of vision, all the above-mentioned structures must be clear and functioning properly so that a dog can see. However, many conditions can affect one or more of the structures discussed earlier and can lead to compromise of vision.
For example, diseases of the cornea (corneal ulcers, dry eye etc) can cause scarring and blur what dogs see. Conditions of the lens, with cataract being the most common problem can lead to obstruction of vision, making a dog visually impaired or blind.
Furthermore, congenital or hereditary problems, injuries later in life or infectious and inflammatory conditions affecting the structures at the back of the eye (the retina and the optic nerve), can cause temporary or even irreversible blindness in some cases.
Early recognition of a problem or a concern is important as in some cases, early intervention can maintain your dog’s sight.
From: Gilger B: Equine ophthalmology, ed 2, St Louis, 2011, Saunders
How dogs see the world?
The way that dogs perceive the world around them, humans, other dogs or other animals is a little bit different to what we see.
As we explained earlier, depending on the dog’s size, their view of the world changes quite a lot. In addition to that, dogs do not see the same colours as we do.
Dogs are able to see colours like blue and green/yellow (and combinations of these colours) but they have difficulty recognising red and green colours.
This is quite similar to a certain type of condition in humans, called achromatopsia (inability to see certain colours). Dogs are born and learn to experience the world around them with blue, green and yellow hues of colours from the beginning of their life and they learn to adapt very well to this.
Concerned about your dog’s eyes?
If your pet experiences one or more of the symptoms above, we are here for you. Request an appointment and get in touch with one of our specialised ophthalmologists.
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