Creeping? Not sure what creeping means? But suspect you are referring to narrowing of the angles to the point where you are are at risk for angle closure which leads to glaucoma.
Slow process. Glaucoma refers to high pressures in the eye. Whether an angle is open or closed refers to the mechanism and can be compared to a sink drain. In closed angle, the drain to the sink is blocked. In open angle, the drain is open, but the pipes are clogged. In someone with risk for angle closure, the angle gradually becomes more closed as a result of a lens inside the eye slowly growing bigger.