with one's eyes open but without noticing or seeing anything

she gazed unseeing across the room

blank unseeing eyes

erase the memory of or no longer register (something unpleasant or distasteful that one has seen or noticed)

when you realize that she bleached her eyebrows, you really can't unsee it

there's a certain photo of him in a shiny tux with green suede loafers that sadly I can't unsee