Pixiv tag help/description: 三白眼 (sanpaku)

Noticed this in a few works of an artist, and it even has a Pixiv Encyclopedia entry.
But I don't know what it is.

Would it be a good tag for us to use?

"When someone's irises are naturally small enough that a large portion of the whites of their eyes are visible."

Here's the Wikipedia article for it.
I wondered why it sounded so familiar; it was a term Gibson used once in Neuromancer.

If we do use this tag, there are the upper and lower sclera to consider.

3-white or 3-sided sclera
lower 3-white (more common than below)
upper 3-white (hint for psycho or horror)
4-white (hint for psycho or horror)