Corneal tissue in the human eye is entirely devoid of blood vessels and instead extracts the oxygen it needs to survive directly from the surrounding air.

A closer look

Corneal tissue in the human eye is entirely devoid of blood vessels and instead extracts the oxygen it needs to survive directly from the surrounding air. This makes it the only part of the human body that bypasses your elaborate cardiovascular system and just breathes the atmosphere all on its own like a weird, transparent little parasite. Of course, this fascinating evolutionary shortcut is also the exact reason why staring at a screen for fourteen hours a day makes your eyes feel like they are coated in sandpaper. Your optical windows are literally suffocating every time you forget to blink while doom-scrolling social media, but at least they don't have to deal with your terrible cholesterol levels