They are the scouts and messengers when magickal divination and messaging is either too risky or not an option, but most importantly, they are the masters of guerilla warfare and hit-and-run tactics. As the name goes, they are the Eyes of the Caedaren nation, and sometimes looks can, well, kill.
The Eyes closer to home are usually the police force when both Bleeders and Hearts are preoccupied (or just plain lazy), while the rest usually are a proud support force that works well with almost any other faction.
Most factions are actually willing to share - and have shared - secrets with the Eyes, who would otherwise likely find out for themselves. Proud, versatile... and quite numerous.