as you mentioned he is not having ROP, but what is refractive correction
if any in his eyes. does he have any squint?
yes less vision can develop amblyopia
and decrease vision in future life, better if he wears spectacles and if vision is less in both eyes then vision stimulating exercises are good.and if vision is less in only one eye then you should start patching therapy.
vision exercises is important.try maximum cooperation as you can have
get his glasses correction if any.