Deathly Siphon

The gaze of your eyes can siphon life force from others to heal your wounds. Make a ranged spell attack against a creature within your reach. On a hit, the target takes 3d6+spellcasting ability necrotic damage, and you regain hit points equal to half the amount of necrotic damage dealt. The target then must roll a constitution saving throw, and on a fail, the spell is completely incompatible with their bodies, triggering them to temporarily go blind. Until the spell ends, you can make the attack again on each of your turns as an action. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d6 for each slot level above 4th.