One of Dracula's Relics.
Appearance in Castlevania: Simon's Quest
Dracula's Eyeball can be found in Brahm's Mansion and allows you to see the locations of hints hidden in breakable walls. It is needed in order to fight Dracula at the end of the game. It is similar in function to the Secret Candle found in the game Vampire Killer.
Appearance in Castlevania: Symphony of the night
The Eye of Vlad is one of the items needed to enter Shaft's chambers. It increases luck by 10.
Appearance in Castlevania: Harmony of Dissonance
The Eye of Vlad is one of the six items needed to enter the ceremonial chambers. It has the ability to negate curses, which was the function of the Heart of Vlad in Castlevania: Symphony of the Night.