Don't put anything but water in anyone's eyes for pepper spray. Not milk. Not antacid. Pepper spray is not an acid and a base will not neutralize it. Nothing will neutralize it. You're not trying to neutralize it; you're trying to remove it. That is how an eye flush works. Just flush it out, away from the nose. It'll still hurt for a while even after it's flushed out.
Spray it from a sports bottle, like cyclists use. A nice wide stream will prevent too much concentration of force that could hurt they eye. Don't use a spray bottle. If you poke a hole in a regular bottle cap, try to make sure it's large enough for a good stream of water to push the pepper spray out of the eye.
The eyes will be squeezed shut reflexively. Don't jam your fingers into someone's eyes to open them. Instead, once you have made sure they're not wearing contacts, press your thumb against the lower edge of the browbone aka the top edge of the eye socket, above the eye, and roll your thumb to pull the eyelid up. (If they are wearing contacts, they have to take them out and throw them away. If they can't, then just guide them to safety but do not flush the eyes and do not attempt to remove the contacts yourself.)
Putting antacids, milk, etc into eyes can cause infection, trigger allergies, or scratch the cornea. Use water. It doesn't matter whether it's saline. It doesn't have to be sterile, as long as it's clean enough that it could be used as drinking water.
