How Do Dogs See in Total Darkness?
How Do Dogs See in Total Darkness?
Dogs have evolved to see well in the dark for hunting, avoiding predators, and navigating their surroundings.
They have many adaptations that help them see better in low light, says Paul Miller, clinical professor of comparative ophthalmology at the University of Wisconsin-Madison.
One of these is a larger pupil, which lets in more light. Another is a center of the retina that has more light-sensitive cells (rods) that work better in dim light than color-detecting cones.
Light-Sensitive Retina
The light-sensitive retina is a vital part of the dog’s eyes that allows them to see in low light conditions. The retina has many different types of rods and cones that help a dog detect motion and make sense of what they are seeing.
It also has a layer of reflective tissue called the tapetum lucidum that helps the dog to utilize light better than humans can in dim conditions. The dog’s rod-dominant retina collects this light and reflects it back to the camera-like lens that focuses what the dog is looking at.
The ability to see in the dark has been a hallmark of dogs since they first came from wild canines that were most active at night or during sunrise. However, while a foundational understanding of the canine visual system is currently available, more research is needed to assess visual capabilities across all dog breeds and to determine any differences between individual, breed, and morphological characteristics.
Tapetum Lucidum
Some animals, including dogs and cats, have a mirrored surface at the back of their eyes that reflects light. This helps them see better at night.
Humans don’t have this mirrored surface, so our eyes can’t see well in total darkness. But many mammals do have it, which is why you might sometimes see a reflective green glow when you look into your dog’s or cat’s eyes at night.
This reflected eye sheen is called “eyeshine.” Animals with this mirrored tapetum lucidum can see in low light because it allows them to reflect light back into the retina. This is a natural adaptation that increases visual sensitivity in dim light conditions.
The tapetum lucidum also helps animals detect motion and shapes better at night. This enhanced nocturnal vision can be helpful to naturalists and hunters, who often use spotlighting techniques at night to spot animals.
Larger Pupil
The black center of your eyes (pupils) change size to control the amount of light that gets into your eye. Your iris, the colored part of your eye, controls this through tiny muscles that contract in bright light and expand in dark light.
Depending on your age and the amount of light, your pupils may shrink in bright light or dilate in dim light. Your pupil may also get smaller when you focus on a close object and widen when you look far away.
Your pupils change size in response to a variety of stimuli, including emotions such as surprise, fear, pain, or excitement. These changes help your pups see to "fight or flight."
Unequal pupils are called anisocoria and can be caused by many different things. They usually develop over time and may not be harmful.
Retinal Photoreceptors
A dog's eyes have retinal photoreceptors, which capture light impulses and transmit them to the brain. This process is similar to human vision.
The retina is located at the back of the eye. It consists of various layers and includes cone photoreceptors, rods, bipolar cells and other neuronal and glial structures.
Cone photoreceptors are responsible for color vision and dogs have two types of cones that recognize wavelengths in the blue-violet range and greenish-yellow range, as opposed to the three primary colors that humans have.
A study conducted in police dogs revealed that the most sensitive dogs were able to detect movement up to 900 meters away in total darkness, whereas humans would need a distance of just 585 meters. This ability, called night vision, is due to a variety of anatomical and chemical factors that allow dogs to see in the dark. However, there is a condition known as progressive retinal atrophy (PRA), which can also affect the photoreceptors.
