Hi andi,
This has been called 'reverse sneezing, which is far from a scientific term. It is not related to anything, like dry air, or allergies, or smells, that I am aware of. It 'just happens'. And the first time, it really gets the owners attention, right?
It has always impressed me, especially when my dogs do it, as an attempt to clear their nasal pharynx, to snort or snuffle out whatever is up there. The white foam is phlegm mixed with air.
Most dogs swallow when they have been successful. In your case, I suspect the phlegm gags him and he up-chucks in response. He may have an unusually large amount of it, I don't know. But there is nothing wrong with him, in this regard.
Anything put into the eye will find it's way into the nasal passages thru the tear duct. This may be having an affect. Hopefully it will abate presently.
I hope this gives at least you some relief.
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