One of my favorite expressions is the "blank circle eyes" (ﾟДﾟ) expression.
I find it being used for a variety of reactions ranging from confusion to surprise, to embarrassment, to amusement.
There are also variants that draw the eyes as blank ovals, and the style varies from the "repeatedly drawn" look to the solid look, but in general, the eyes are blanks with no colored irises.
It's also quite prevalent in manga, though I don't have any ready examples at the moment.