What do you think of this fact?
Take a deep breath. Your lungs grab the oxygen, your blood ships it around your body. Almost everywhere, anyway. One part of you skips the blood entirely and helps itself straight from the air: your cornea.
See-through means no blood vessels
The cornea is the clear structure at the very front of your eye. According to StatPearls, it is “avascular”, meaning it has no blood vessels. The reason is simple: it has to stay crystal clear so light gets bent properly. Vessels running through it would be about as helpful as a tangle of cables in front of a camera lens. Africa Check sums it up: if the cornea contained blood, we would be blind.
But even cells without vessels need oxygen. So the outermost layer of the cornea simply absorbs it from the environment. Nutrients come from your tear fluid and from the aqueous humour, the clear liquid in the space in front of the iris and lens.
Nearly all of its oxygen comes from the air
How much really comes from the air? In 2023, a research team measured it with a tiny optic fiber sensor, mostly in mice. Their conclusion: uptake from the atmosphere accounts for “virtually all” of the oxygen the cornea consumes. Only at the edge do nearby blood vessels chip in, and the study calls that contribution negligible.
That is exactly why oxygen comes up with contact lenses. According to Africa Check, a lens reduces the oxygen supply to the cornea, making it swell. Wearing lenses overnight cuts the amount down even further.
Tiny, but ridiculously sensitive
No blood vessels doesn’t mean no nerves. Quite the opposite: StatPearls calls the human cornea the most richly innervated tissue in the body, with a sensitivity 300 to 600 times that of skin.
In 1998, eye researcher David Maurice proposed an odd hypothesis: the rapid eye movements of REM sleep might mainly be there to keep the aqueous humour moving while your eyelids are shut, so the cornea gets enough oxygen. He called it the “stagnant aqueous humour hypothesis”.
So you don’t just breathe with your lungs. In a tiny way, you breathe with your eyes too.