In glaucoma, the past 3 years my mother's eye pressure has not been controlled with drops or laser & she has lost vision. Why the lack of control?

Every Eye Differs. While most patients are controlled with drops and laser, not all are. When medicines and laser are inadequate, surgery is usually required.
Tough disease. Not all glaucoma is created equally. Most patients can be controlled with drops or laser. However, incisional surgery is needed in some cases. If there is true progression of vision loss, additional treatment is needed.