If stinging, I've always found it's due to the sweat on my head/forehead, and not the rain itself per se.

About the only solution I've had is: a rain 'cap' on the helmet itself, to keep the water from getting onto my head and draining the salt/rain into my eyes. Works better than eyewear, so far as I've found. In mild misting and light rain, I've had eyewear work okay, but the moment it gets heavier or the ride is longer then keeping the rain off my head seems to work better.

YMMV