system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does a new pair of glasses temporarily distort your depth perception? What causes this?
gpt
Glasses have two effects: focus, and magnification.

The focus is what you want to change.  The reason you need glasses is that your eyes are miscalibrated, and they need a focus adjustment.

The magnification is a side effect and generally not wanted.  It's the reason that people with powerful lenses look like their eyes are either way too small (nearsighted) or way too big (farsighted) - the lens is changing the apparent size of their eyes.  The reverse happens, too: your new glasses are putting objects in focus, but they're also distorting their apparent size.  If you're nearsighted and you just got a more powerful prescription, objects look slightly smaller than they used to.  That messes with your depth perception, because your brain thinks everything is slightly farther away than it is.

The depth perception distortion will go away as your brain adjusts to the new relationship between how big something looks and how far away it is.