One of the big reasons that open-angle glaucoma can cause severe damage is that it has no symptoms in the early stages. It causes no pain and vision stays normal. It’s an important reason why you should have your eyes checked annually.
Without treatment, people with glaucoma will slowly lose their peripheral vision. If it remains untreated, people may actually miss objects to the side and out of the corner of their eye. Over time, the central vision (looking straight-ahead) may also decrease.