The human eye is a biological wonder. Able to perceive the subtle hues of 1 million colors and filled with tens of millions of photosensitive rods and cones, our eyes help interpret reality for us — but they’d be useless without a muscle called the orbicularis oculi. A sphincter muscle arranged in concentric bands around both eyelids, the orbicularis oculi controls blinking, and drains tears from the eye to the nasolacrimal duct system (which eventually drains into the nasal cavity). These functions are essential to happy and healthy eyes, as they clear particles from the surface, lubricate the eyes, and supply oxygen to the corneas. Without this crucial muscle, our corneas would swell, our eyes would dry out, and eventually we’d go blind.
However, the orbicularis oculi boasts another impressive biological accolade — out of all 650 or so muscles in the human body, it’s the fastest one. This muscle can contract, or blink, in as little as 0.1 second. Although blinking is incredibly quick, the average person will blink up to 19,200 times per day — which takes up about 10% of a person’s waking hours.
When someone spots something others can’t see, they’re often called “eagle-eyed.” Turns out, that’s a biologically appropriate compliment. Raptors, including bald eagles and golden eagles, have some of the best vision in the animal kingdom. These birds of prey can see four to five times farther than humans. This 20/4 vision (meaning eagles see 20 feet away what humans see 4 feet away) is like being able to spot an ant on the ground from a 10-story building, according to LiveScience. Some experts believe an eagle’s incredibly deep fovea, located in the back of their eyes, essentially allows these birds to use their eyes like a telephoto lens. This comes in handy when eagles glide on the wind looking for unsuspecting prey hundreds of feet below.