You may have heard that dogs have remarkable night vision, but can they actually see in the dark? Many owners leave lights on for their dogs when they are gone at night and even feel bad if they accidentally leave their dogs in the dark. But your dog probably doesn't mind the dark. Your dog's vision is more advanced than you may realize.
Can Dogs See in the Dark?
Dogs are able to see much better than humans in low-light conditions. While they cannot see much in absolute darkness, they can see quite well in dark conditions where only the smallest amounts of light are present. Canine eyes are able to take in small amounts of light and process images that humans would never see in the dark. A nightlight, streetlight, flashlight, or even the moon and stars can provide enough light for dogs to see almost as well as they see in bright light.
How Dogs See in Low Light
On the surface, a dog's eye may seem much like the eye of a human. However, there are some very important differences in the structure of a dog's eye that give them superior night vision.
Animal and human eyes are able to receive images in similar ways: light enters the eye through the cornea, which bends the light to help focus the image. Some of the light passes through the pupil—how much depends on the opening of the pupil. The muscles in the iris control how dilated or constricted the pupils are depending on light conditions. A dog's pupil opens wider than a human's pupil, allowing more light in.
Light passes through the lens of the eye, a structure that focuses light through the vitreous humor onto the retina. The lens is responsible for focusing images at varying distances. A dog's lens is closer to the retina than a human's lens, which makes images brighter.
Next, the light hits the retina, where photoreceptors such as rods and cones process the image and send signals to the brain. Rods are responsible for processing images in low light. Cones are responsible for color vision and are less sensitive to light than rods.
There are rods and cones in the retinas of both humans and dogs, but the amounts differ between the species. A human retina contains more rods than cones, enabling people to see vivid color in bright light and very little in low light. A canine retina has many more rods than cones, indicating that dogs do not see vivid colors, but they can see images much clearer in dim light.
Dogs have something that humans lack: mirror-like tissue in the back of their eyes called the tapetum lucidum. This structure gives the retina an extra opportunity to register the light that has entered the eye. The tapetum also scatters light, so these images may not be as clear as they would be in bright light.
You may have noticed your dog's tapetum when you take a flash photo or look at your dog's eyes in the dark. This is why dog's eyes appear to glow in the dark.
What to Do If Your Dog's Night Vision Is Poor
Some dogs seem to see better in the dark than others, but it's safe to say that most see much better than humans. If you think your dog doesn't see well at night, there may be an eye-related reason for it. If you notice that your dog used to see well in the dark but now struggles with night vision, there could be an eye problem causing vision loss.
Many dogs experience some degree of vision loss as they age. At first, you may notice this vision loss more at night than during the day. Age-related eye changes such as lenticular sclerosis can limit a dog's eyesight, especially in dim light. Cataracts may develop and progressively worsen, causing loss of eyesight that is more noticeable in darker conditions.
Contact your veterinarian if your dog's vision seems to be changing. Your vet may be able to determine the cause and offer treatment that can prevent blindness.