#helms

"I need armor for the tourney," Dunk told him. "A suit of good mail, with gorget, greaves, and greathelm." The old man's halfhelm would fit his head, but he wanted more protection for his face than a nasal bar alone could provide.

From that description I think's likely this sort of style which gives a good amount of visibility as you can see

VS

the "classic" greathelm

Now the from the gif I can see the helm he has is less severe but still quite a reduction of the field of visibility compared the halfhelm I assume he had training or experience with.

gif source

I've only sparred with...ugh the precise helm name escapes me....skull cap equivalent helm at most, but I've goofed around in a great helm at least once and uh it's a learning curve navigating in them. Even if you have good body awareness your compensation for reduced visibility isn't that great. I was told it gets better over time with practice, but the breathing is always going to suck and can even lead to rusting if you're not careful with upkeep of the metal. Also if you think you're going to puke and don't think you can get it off in time do NOT bend over to heave.

Helms of Morrowind

Concept art for The Elder Scrolls III: Morrowind