Their only defense is in response to a missed melee attack. Therefore an easy way to kill them is to throw something, such as a [[Swords|dagger]], zap them with an attack [[Wands|wand]] or even vomit on them. As long as you don't attempt to melee them they can cause no harm.

It is also possible only safe to safely engage in melee with an eye if you ''can't see'' its stare; [[Wand of Invisibility|turning the eye invisible]] or fighting in darkness will solve this problem (though the latter may surely come with its own risks).