How do we switch focus between our eyes? (e.g. when you hold a card to your nose and choose to see one side or the other)

Question

There’s plenty of information online about how the eye changes lens shape for physically focusing the light from different distances, but how do we switch which eye is dominant in our vision? Is it purely in the ‘software’ of our brains, or is there something going on in the ‘hardware’ before our brains get the signal to process?

E.g. Holding a card to your nose and choosing which side to view, or looking through a scope with both eyes open and choosing to see the scope image or the unmagnified image from your other eye.

In: 2

Answer 1

As far as I know, your lens muscles control the lens, which is responsible for focus.

The muscles essentially constrict, which changes the shape of the lense, and focuses at a different depth of field