Here's why:
* Breed: Some dog breeds are known for having dark eyes, like the Doberman Pinscher, Rottweiler, or the Black Labrador Retriever. Their dark eyes are a defining feature of their breed.
* Pigmentation: The color of a dog's eyes is determined by the amount of melanin in the iris. Dogs with a lot of melanin in their irises will have darker eyes, including completely black ones.
However, it's important to note:
* Health: If a dog's eye color changes suddenly or drastically, it could be a sign of an underlying health issue. If you notice any changes in your dog's eye color, especially if accompanied by other symptoms, it's important to consult with your veterinarian.
In short, completely black eyes in a dog are often just a normal breed characteristic or due to pigmentation. But any sudden changes should be checked by a veterinarian.