What is happening in/to my eyes when my focus switches from content on my screen to the reflection on my screen?
In: Biology
Your pupil contracts or expands, like a ballon where you pull or push on two ends simultanisly.
Since your pupil is filled with a fluid which breaks light in other ways than air does and your pupil is shaped in a special way, your brain can focus the light from all objects to be sharp on your retina.
Sounds like a [saccade](https://en.m.wikipedia.org/wiki/Saccade). Your eye is mapping all the interesting things going on on the screen.
Your eyes have a lens inside them, very similar to what you find on reading spectacles.
This lens takes light rays hitting it, and focusses them into a single sharp image. To see something clearly, you want that image to land exactly on your light sensors at the back of your eyeball.
When you look at objects near and far to you, that image shifts.
So your eyeball stretches or compresses that lens to ensure that the image always falls exactly on your light sensors.
The pupils also change size, but that doesn’t actually help with making the image sharp, it just comes together with it as part of the package.
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