Dogs see the world as deuteranopes.
Dogs are known for having two types of functioning cone cells in the eye which allows them to see color. This makes dogs dichromates. Humans, on the other hand, have three and that makes them trichromats. One may compare a dog's perception of color as being roughly similar to that of a person who is red-green color blind (a deuteranope). Just like a deuteranope, dogs have a hard time discriminating between red and green. However, they have a much better time detecting yellow and blue. This explains why in the sport of agility, you often see many agility obstacles featuring the colors blue and yellow.
Dogs see better in the dark because they have a history as crepuscular hunters.
It is estimated that dogs are capable of seeing in light that is five times dimmer than what a human can see. Dogs see better in dim light because of their evolutionary past as crepuscular hunters. A dog's ancestors indeed fed on critters that were mostly active during crepuscular times, at dusk and dawn.
Your dog's pupil is just a black hole.
When you look into your dog's eye, the pupil looks like a black circle, but in reality, the pupil is just a black hole that appears to be black due to the presence of special light-absorbing pigments located in the interior portions of the eye. The same applies to the pupils of humans and other animals.
Dogs don't have eyebrows like humans do.
Dogs do not have eyebrows in the real sense of the word for the simple fact that they don't need them. Eyebrows in humans are there for one main reason: to prevent salty sweat from falling down the forehead into the eyes. Dogs do not need eyebrows because they don't sweat as humans do!
Dogs have whiskers over their eyes for an important purpose.
Those whiskers above your dog's eyes are known as supraorbital whiskers and they play a very important role: protect your dog's eyes from being poked and injured by sticks, brush, debris and even an owner's fingers. Upon detecting something making contact with these whiskers, indeed, the dog's "blink reflex" will jump into action eliciting the eyes to close so to prevent them from getting accidentally scratched or poked.
Dogs use their eyes in communication.
Pay attention to what your dog's eyes are saying. When dogs are super satisfied with something, they'll show squinty eyes almost as if daydreaming. When dogs are worried about something, they may show the white of the eyes (whale eyes). Whale eyes are often seen in dogs who turn their heads but want to keep an eye on what is going on as they do this.