Oculus

A round, central opening or "eye" in a dome.(pr. AH-cyə-ləs)Example:Interior view of the Pantheon, Rome, 118 CE. At the top of the Pantheon's coffered dome is its oculus. In this photo, sunlight projects through this open hole to the sky. There has never been any glass or other cover on this opening. Anticipating the rains, the Romans placed twenty-two small drains in the floor. They continue to function well today.Also see circle, fenestration, lantern, lunette, omphalos, and pantheon.