Unlike most quest-related items, this will continue to drop beyond the amount needed for the Related Quests. Some will drop even when you do not have one of the listed Related Quests. This allows you to build up a supply of this item for future use.
Although this does not always drop, between killing the 5 Dark Night Gargoyles you also need for [50][Daily] Support the Front Lines: Eliminate the Gargoyles, plus any that get in your way while doing [50][Daily] Twisted Soul, you should quickly build up a stockpile of these eyes so that you never have to think about having the 5 you need.
