August is National Eye Exam Month, so I wanted to take the opportunity to address some of the questions I’m commonly asked as a veterinary ophthalmologist.
“Do dogs see in color?” “Why can my dog / cat see so well at night?” “Can dogs watch TV?”
“Do dogs see in color?”
Dogs do, in fact, see in color, but their visual spectrum is limited. They have trouble differentiating between hues on the red and green spectrum, but they can see other colors well. Remember: the next time you buy a toy for your dog, pick one in a color he or she can see!
Cats, on the other hand, are considered trichromatic, meaning that they see similar color patterns as people. Birds have tetrachromatic vision, enabling them to see additional wavelengths of light that people cannot see, such as color hues in the ultraviolet range. We can only imagine the array of colors birds can see!
“Why can my dog / cat see so well at night?”
Dogs and cats have much better vision at night than humans. There are two reasons for this:
- First, dogs and cats have a higher concentration of photoreceptors called “rods” in their retina, which allow for better vision in dim / dark lighting.
- And secondly, they have a reflective layer in the back of the eye near the retina called the tapetum lucidum (it’s the reason your dog or cat’s eyes look green / yellow / orange / blue when you take a picture or shine a light into their eyes).
It is believed that the tapetum lucidum acts almost like a layer of shiny tin foil, allowing the light that already passed to the retina for vision to bounce off the tapetum lucidum and strike the retina again. In essence, the retina gets to see the same low level of light twice, increasing vision when it is dark.
But this night vision comes at a price: the daytime visual acuity of dogs is less than that of people. Their vision is thought to be about 20/65, as compared to the 20/20 vision in humans.
“Can dogs watch TV?”
Studies suggest that dogs most likely cannot make out a clear image of the TV. The answer to this question is related to a concept known as Critical Flicker Frequency (CFF). The idea of CFF is this: when light is flashing, humans can distinguish the individual flashes; however, as the frequency of the flashes increases, the individual flashes become difficult to distinguish. At some point, we will not be able to distinguish between individual flashes, and we will instead see a solid image.
This is how TV works: a series of flashes comes through to our TV at a very quick rate. The rate is so fast that we cannot distinguish individual frames, and instead see a single fluid yet changing image of the show we are watching (likely “The Simpsons” if it’s my TV).
Naturally, the refresh rate of the TV image is set to a level similar to the CFF of people, but dogs have a higher CFF level than we do. This means that when I watch “The Simpsons” on my TV, my dog Cooper is likely just seeing a flickering of images on the screen. I am left to assume she still likes to watch it for the audible jokes.
Having said this, I hear people say all the time that their dog loves to watch certain people / shows / things on TV. So, while the studies say dogs likely cannot make out a clear image of the TV, some may see just enough to get excited about what they see. Others believe that the new technology of TV (LED, LCD, and plasma screens) have a faster refresh rate that does allow dogs to now watch TV!