The spear Visions of the Absolute has the ability: Absolute Night: Chance to Blind target. Deals an additional 2d6 Piercing to certain creatures that sport multiple sets of eyes.
So why doesn't it work against spiders (specifically the extra damage), according to the interweb “About 99% of spiders have eight eyes. Some have six, four, or two.”
If it's only meant to works against Beholder Kin then I think you description should be improved, please.
