This video does a nice job of highlighting some weird aspects of human vision in just three minutes.

This first oddness it mentions is the blind spot, a place on the retina devoid of imaging cells where the optic nerve (which is really a big bundle of nerves) meets the eye. This is even stranger than the video suggests, because the optic nerve doesn’t just make contact there, it passes through the back of the eye so its various fibers can spread out across the retina and connect up with the light-sensitive rod and cone cells from the front.

This is true not just of human eyes but the eyes of all vertebrates — fish, amphibians, reptiles, birds, and mammals, so you might suppose that there’s some necessary reason for it. But it’s not true of the eyes of a squid, octopus, or cuttlefish, that is, the cephalopods. Their optic nerves connect up to light-sensitive cells from the back, so there’s no need for a blind spot.

So why don’t vertebrate eyes work the same way? It’s probably just another of several examples of evolutionary accidents, things that seems bizarre from an engineering standpoint but are what you’d expect given evolutionary development.

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