Through the eyes of a dog
Have you ever wondered how your dog views the world? In this article, clinical animal behaviourist Becka delves into the structure of a dog's eyes and how this supports dogs in perceiving and responding to their environment.
Dogs use their sense of sight as a means of gathering information about their surroundings. A dog's response to this information may vary depending on the individual; nonetheless, some element of body language will be displayed to convey their emotional state, prevent conflict and develop or maintain social bonds. To understand how dogs use their eyes to learn about their environment and to communicate, a familiarity with their anatomy and physiology is beneficial.
The eyes are specialised sensory organs; they contain several sophisticated structures which work together and function to provide animals with the sense of sight. Dogs have a large cornea and lens; the cornea acts as a window, controlling the entry of light into the eye and directing it towards the lens, which focuses light onto the retina, allowing dogs to see in lower light levels.
The retina contains specialised photoreceptor cells called cones and rods, these filter and convert light into electrical signals which are interpreted by the brain to create an image. Cones detect colour; dogs have less cones than humans; as a result, they see fewer colours. Dogs see shades of yellow, blue and combinations of these colours, suggesting that their vision is mostly greyish-brown. Rods detect light; dogs have a greater number of rods than humans, allowing them to see better in the dark. Dogs also have a reflective structure called the tapetum lucidum, a mirror-like layer behind the retina, which reflects light back towards photoreceptors, further enhancing vision in lower light levels; this appears to glow in colours ranging from green, blue and yellow.
The pupil, a black circular-like structure in the centre of the eye, acts as an opening which dilates (enlarges) or constricts (narrows) to control the amount of light that enters the eye. In lower light levels, the pupils will be larger, allowing more light to enter; this is relevant to dogs since they are a naturally crepuscular species, which means they are most active at dawn and dusk; however, dogs have developed sleeping habits that accommodate the lifestyle of humans. A fearful or excited dog may have larger pupils, allowing them to take in more light and respond appropriately to their surroundings, for example, to find an escape route or to catch their favourite toy.
When a dog feels stressed or fearful, their facial muscles become tense, pulling the skin backwards and causing the sclera, the white part of the eye, to look more prominent. A fearful dog may turn away to avert eye contact and avoid conflict, or may stare out of the corner of their eye, exposing the sclera, often referred to as the whale eye. A nervous dog may squint or frown with minimal blinking to communicate their discomfort to another dog or person, although this is often missed by humans and can result in bites. Nonetheless, mutual eye contact between a dog and caregiver can stimulate the release of oxytocin, known as the love hormone; slow blinking may be noted in this situation and is thought to be associated with positive social interactions.
The dog's eyes are positioned to the side of their face, which provides them with a greater field of vision; however, they have a blind spot above their eyes, which can cause them to become startled when humans pat them on their head. Moreover, dogs have reduced depth perception, the ability to gauge distance, compared with humans; for this reason, they may appear uneasy when they see objects or movement right in front of their face or far in the distance and may find stairs challenging.
Sudden changes in behaviour can indicate underlying physical health complaints and may warrant a veterinary visit. However, some behaviours that appear strange to us may be normal for our dogs; try to view the world through their eyes, what do you see?
A close up photo of Becka’s dogs eye. The pupil can be seen as the darkened circle in the middle of the eye, a light was shone into the eye to obtain this photo, thus the pupil is narrowed and the brown coloured part of the eye is the iris. The other parts of the eye can not be seen in this photo, however, are functioning to allow the dog to see.
A close-up photograph of Becka’s dogs iris. you can see the colouration of the iris and the pupil in the middle of the eye. Photo courtesy of Iris Galerie Jersey.
