Dogs can see yellow and green hues’ but they can’t distinguish red from green — a similar situation to humans who are red-green color-blind. However, dogs may be more sensitive to ultraviolet light than humans are, according to 2014 research, in which case they would be better at sensing a wider ranges of blues than people are.
Dog vision is almost three times blurrier than human vision, according to a 2017 study. In that research, whippets, pugs and Shetland sheepdogs were trained with treats to distinguish lines that were different distances from one another. These lines were then used to give the dogs a visual test, not unlike the alphabet chart a human might see during a visit to the eye doctor. Dogs had about 20/50 vision, the study found, meaning that something a human could see clearly at a distance of 50 feet (15 meters), a dog could see clearly at 20 feet (6 m). Dogs, however, do see better than people in dim light, according to the merck manual for vrterinary medicine and can see movement better, too. One special feature that magnifies light to a dog’s eye is the tapetum lucidum, a reflective layer that also gives dogs their characteristic eyeshine at night.
Hearing and smell are where dogs really shine. According to the Merck Manual, dogs hear about four times better than humans do. Incredibly, their sense of smell is a whopping thousand to ten thousand times better than ours. The olfactory center of a dog’s brain is 40 times the size of the olfactory center in a human’s brain. Because dogs can distinguish between smells with great sensitivity, they have been trained to sniff out human diseases: researchers discovered in the early 2000s that dogs can sniff out signs of early stage cancers and in 2021 scientists found that dogs could identify Covid-19 in the scent of urine samples, Live Science previously reported.
