Presumably they can be adjusted to only provide the minimum amount of correction necessary for the user's eyes to achieve correct focus, thus having the eye mus

Presumably they can be adjusted to only provide the minimum amount of correction necessary for the user's eyes to achieve correct focus, thus having the eye muscles always relaxed. Only if the glasses detect something far away would it be adjusting itself to the "strongest" power. At intermediate ranges it would be using an intermediate power, and if the distance is something that you can read without correction it would become a (non-prescription) lens.