You put on someone else’s glasses, and suddenly everything looks strange and wrong.

Or you take off your own glasses, and the words in your book turn fuzzy and hard to read.

It feels like your eyes forgot how to see properly.

But your eyes didn’t forget anything.

Inside your eye, light has to land in exactly the right place to make a clear picture.

And when it lands a little too early or a little too late, everything looks blurry.

So what are glasses actually doing to the light before it reaches your eye?