Always Check Your Blind Spot
(Check the end of this post for a cool way to test your eyes’ blind spot!)
Humans have fairly good vision, as the animal world goes. Perhaps not as advanced as some ultraviolet-sensing birds or the super-seeing mantis shrimp, which can see circularly polarized light from UV to infrared, but pretty good. But along the evolutionary path that our eyes took to become what they are today, they left a blind spot … literally.
The rod and cone cells that make up the light-sensing part of the retina are wired from the inside, like a camera whose interior is filled with wires. All of those wires have to exit out the back of the eye, leaving a tiny hole in the retina where you can’t see anything:
Our eyes are on the left in the image above. The eyes on the right? Cephalopod eyes, like those of squid, have retinas that are wired from beneath and don’t have a blind spot. This is probably why we are doomed to be conquered by them …
Want to test your blind spot? Open up the “R/L" image at the top of this post, then close your right eye. Stare at the letter "L" with your left eye and move your head closer and farther from the screen to watch the other letter disappear.
Rinse, repeat, freak out.