It is also a requirement for international flight operations under ICAO regulations. I’m pretty sure this regulation (or something close to it) is enforced by just about every flight-licensing authority worldwide.

It’s plain good sense and I’m glad it’s in there. A plane cannot pull over to the side of the highway while the pilot fumbles around trying to dig his glasses out from under the seat :)

(As a side note, this rule isn’t just for dropped spectacles: there have been cases where they literally get sucked out of the airplane if a cockpit window fails or where a bird strike causing facial injuries also damages the pilots glasses).

If you want to talk specifics, you’re supposed to be able to see your speed and how your car is performing. You should be prepared for contingencies, like your temperature changing or a yellow/red warning on the dash. You may need to deal with a problem in the car, like grabbing something that could slide under the pedals.

The same goes for farsighted driving. Yes, in most cases you could just follow traffic and you wouldn’t need to read street signs or look at traffic a mile ahead. But you need to be prepared for unexpected situations, and you’ll generally do worse just mentally managing your reduced vision.

I’ve driven without my glasses and tested an unexpectedly bad trial prescription in a car, if it matters.