In the Afterbirth DLC there is a new feature called Greed Mode.
According to the Rebirth wikia:
Each floor has a Curse Room, a Devil Room, a double-wide Shop, and an exit room all connected to a main double-height arena room with a button in the center. An already unlocked Treasure Room with a silver doorframe and a normal locked treasure room are also available.
In the shop, however, it's possible to buy the X-Ray Vision item, which reveals and opens all Secret Room and Super Secret Room entrances.
Before I waste my money, are there any Secret Room in the Greed Mode?
The Greed Mode wikia page now states that:
The level may also contain a Secret Room