I had (and still have) a similar problem in winter where I am living in Finland. My head shape means I have trouble finding helmets that fit well. I had been using an Abus one which fitted me well and needed replacing so I decided to try their InVizz one which has a hidden sliding visor.

It helped a bit, but there is still quite a bit of airflow around the sides of, and under the visor, as well as through the helmet vents. Eyes still watered on cold days. A raincover reduces the ventilation from above, and it is possible to wear glasses under the visor to cut out more of the wind.

The winter was not particularly cold (a few weeks of -5C to -10C) so I eventually went back to my usual cycling glasses and a normal helmet. The InVizz one was a little bit annoying on a road/touring bike - it juts out a little bit further and lower than normal helmets at your forehead, which I didn't like. It seemed to be slightly larger-sized than my previous Abus one (which was also a size "large") so there was a gap between the plastic cradle and the helmet shell, maybe raising airflow through the vents. It is nice to have no obstructions for your vision though.

If we get a bad winter this year (-20C region) I'll try it again.