What changes occur, as you are driving a car, when you look down at the speedometer and then back at the road?

Question

medical

Answer 1

Assuming binocular vision,

The eyes move vertically and also converge, requiring co-ordinated movement of the intraocular muscles.
And the reverse when reverting to distance vision.
The eyelids will move vertically to a lesser degree in concert with this.
The ciliary muscles of the eyes will tense to provide the refocussing of the lenses, "accommodation" to suit the dashboard viewing distance, and then relax.

Pupil size may change if a marked illumination shift is present: glancing away from a sunny road, for example.

To avoid that diverted gaze, and muscular delay and effort, many military aircraft have "head-up" displays, where instrument readings are projected out *as though* at infinity.
It's been tried with car speedometers, but hasn't become standard, yet.