Here's what's happening where you can't see it.
The back of your eye is one of the hungriest tissues in your body.
Ounce for ounce, it burns oxygen faster than almost anything you own. And it sits in front of a nonstop flood of light (sun, screens, kitchen lights, headlights) every waking hour.
Light plus oxygen throws off sparks. Scientists call them free radicals.
The damage they cause is called oxidative stress.
Picture a campfire, with embers drifting onto the cells that let you see. All day. Every day. For decades.
Every one of those cells is wrapped in a thin wall made of delicate fat. The ones that sense light are built from stacks of it, like a roll of coins.
And delicate fat is exactly what those embers scorch first.
Your eyes fight back.
Every day, those cells shed about a tenth of their tips and rebuild them.
A cleanup crew hauls away the damaged pieces overnight.
At 25, the crew keeps up easily.
But after decades of sun and years of screens, the embers start landing faster than the crew can clear them.
The walls wear thin. And your eyes get slower at everything: focusing, refocusing, bouncing back from bright light.
It isn't a disease. It's wear.
And it doesn't reverse itself on its own.
That's why, if you've felt it creeping in, the evenings you give up keep adding up.
First you stop driving after dark. Then you stop saying yes to things that end after dark.
Then you're planning your whole week around the sunset.