So the Eye of Corruption tooltip says it lasts 8 seconds and does damage EVERY 2 SECONDS yet it does damage every second which gives everyone 8 stacks of the eye debuff per proc rather than 4 like the tooltip says it should be with the timing. Please look into either the tooltip being bugged or if the effect is doing damage twice as often as it should be.
I believe it depends on your corruption. It’ll tick faster if your corruption is higher, but I could be wrong. That or it for some reason goes based off Haste? 
I have always gotten 8 stacks of the debuff even at only 25 corruption while my higher corruption toons closer to 60 also get 8 stacks per eye. If it was based on haste my DH would get like 16 stacks whenever one popped while in demon form and my monk doesn’t even have 15% haste.